Make video projects, with a moving channel split as the first video effect

A project can now be a clip: Setup has a Video switch with a length, a frame rate and presets that set the canvas too (Instagram story, reel and feed video, TikTok / YouTube Short, Square loop, Full HD clip). The preview renders the whole clip, shrunk to a memory budget, and loops it with play/pause and a scale; Save As... renders it again at full size and pipes the frames into ffmpeg as .mp4, .mov, .mkv, .webm or .gif, with a progress window that can cancel. --duration, --fps and --video-preset do the same from the command line. Effects learn about time through FrameTime and Effect::renderFrame, which falls back to render, so nothing that holds still changes. Channel split now sways, shakes and rolls a tracking bar down the picture in a video; its motion params are marked forVideo() and hidden in a still project, and a still renders byte for byte as before. renderFrames starts every frame from the same seed and renders the still stages ahead of the first moving one only once. The version moves to 0.6.0. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Give Effector its own icon
2026-09-26 11:22:01 +02:00 · 2026-09-26 10:38:49 +02:00
30 changed files with 1952 additions and 41 deletions
@@ -4,6 +4,31 @@ Every release of Effector, newest first. The version lives in one place, the
 `project()` line of `CMakeLists.txt`, and each release is a `vX.Y.Z` tag on the
 commit that made it. The interface shows this file under Changelog in its menu.
 ## [0.6.0] - 2026-09-26
 ### Added
 - Video projects: switch Video on under Setup and give the clip a length and a
  frame rate, or pick a preset that sets the canvas too: Instagram story,
  Instagram reel, Instagram feed video, TikTok / YouTube Short, Square loop and
  Full HD clip. The preview renders the clip and loops it, with play/pause and
  a scale to look at any one frame.
 - Save As… writes a video project as `.mp4`, `.mov`, `.mkv`, `.webm` or `.gif`
  through `ffmpeg`, with a progress window that can cancel it.
 - Channel split moves in a video: its channels sway, shake from frame to frame
  and a tracking bar rolls down the picture, like an old tape on a tube. The
  new Wobble, Jitter and Tracking bar settings show only in a video, and a
  still renders exactly as before.
 - `--duration`, `--fps` and `--video-preset` render a video from the command
  line.
 - A Vertical Full HD canvas format, 1080 × 1920.
 ## [0.5.3] - 2026-09-26
 ### Added
 - Effector has its own icon, an E split into its colour channels, in the app
  menu, the dock and About Effector; a one-colour version goes with it for
  panels.
 ## [0.5.2] - 2026-09-26
 ### Changed
@@ -15,7 +15,9 @@ Everything is warning-clean under `-Wall -Wextra -Wpedantic`; keep it that way.
 The core test suite is a single hand-rolled binary (no framework), so there is no
 per-test filter: run `./build/tests/effector_tests` directly to see the section
 headings (`rng`, `registry`, `scanlines`, `tiles`, `blur`, `chain`, `project`,
-`image io`, `batch loading`) and the `ok`/`FAIL` lines. To iterate on one area, comment
+`image io`, `batch loading`, `video`, `version`) and the `ok`/`FAIL` lines. The
 `video` section writes real files through `ffmpeg` when it is on the PATH and
 prints a `skip` line otherwise. To iterate on one area, comment
 out the other blocks in `tests/core_tests.cpp` or add a new
 `std::cout << "section\n"` block — checks are plain
 `check(condition, "description")` calls and `main()` returns the failure count.
@@ -170,11 +172,56 @@ the `effector` application name on each entry; the GUI tests point
 `XDG_DATA_HOME` at a temporary folder so they never touch the user's list. Opening one replaces the sources, so a decode still in flight
 is discarded rather than mixed into the new project (`dropLoadedImages_`).
 ### Video projects
 A project is a still or a clip: `VideoSettings` (`src/core/video.hpp`: enabled,
 duration, fps, preset) rides in `Project::video` and `Options::video`, and is
 written to the project file only when enabled. `videoPresets()` is one table
 like `canvasFormats()` — a preset names a canvas format plus a length and rate,
 and like a format it is the presentation, never the truth: the render goes by
 duration and fps. Adding a preset is a line there.
 Time reaches an effect as a `FrameTime` (`src/core/effect.hpp`; the default,
 `fps == 0`, is a still) through `Effect::renderFrame`, which falls back to
 `render` — an effect that does not move overrides nothing. One that moves
 overrides `renderFrame` and `animated(values)`, and marks its motion params
 `.forVideo()`: the interface hides those in a still project (declaratively,
 like `.styled()`), the CLI still has their flags. A still must render byte for
 byte what it did before the effect learned to move.
 `renderFrames` (`src/core/chain.cpp`) renders a clip. Every frame starts from
 `Rng(seed)`, so a stage that does not move draws the same values every frame
 and holds still. A moving effect must therefore leave the shared rng in the
 same state on every frame — the channel split draws its per-frame shake from a
 generator of its own, seeded by one draw — or everything after it would flicker.
 The stages before the first `animated()` one are rendered once and their image
 and rng state reused; the `video` tests assert that frame k is exactly
 `renderChain(..., FrameTime{k, ...})`, so that shortcut can never change output.
 The determinism contract covers the frames; the encoded file is whatever the
 machine's ffmpeg makes of them.
 `VideoWriter` pipes raw `rgb24` frames into the `ffmpeg` program
 (`posix_spawnp` with an argv — no shell; `SIGPIPE` ignored; stderr captured for
 the error message; codec by extension). `cancel()` SIGKILLs it — SIGTERM makes
 ffmpeg flush its encoder first — and removes the file; a writer destroyed
 unfinished cancels itself.
 In the interface, a video render (`startRender`) renders every frame at full
 size, shrinks each (`Image::scaledToFit`, sized by `clipSide` to a memory
 budget) and hands them over through `pendingFrames_`/`clipProgress_`; the
 clip on screen keeps looping until the new one is complete, and
 `renderCancel_` stops a clip whose settings went stale. Save As… renders again
 at full size on `exporter_` into a `VideoWriter`, with an `exportWindow_`
 progress window (its `exportBar_` nulled in `closeExportWindow()`). Under Xvfb
 the GTK file dialog goes through the desktop portal and may open on the real
 session instead; set `GDK_DEBUG=no-portals` to keep it in the Xvfb display.
 ### Two link targets, deliberately
-`effector_core` (static) holds image IO, params, effects, rng and links only
+`effector_core` (static) holds image IO, params, effects, rng, video writing
-`gdk-pixbuf-2.0`, `pangocairo` (the text effect's glyphs; Pango and Cairo need
+and links only `gdk-pixbuf-2.0`, `pangocairo` (the text effect's glyphs; Pango
-no display) + Threads — **no gtkmm, no display**. `effector_gui` (static) adds
+and Cairo need no display) + Threads — **no gtkmm, no display**; `ffmpeg` is a
 program it runs, not a library it links. `effector_gui` (static) adds
 `src/cli/` and `src/gui/` and links gtkmm, and the `effector` executable is
 `src/main.cpp` on top of it; the GUI tests link `effector_gui` too. Keep GTK out of
 `src/core/` and `src/effects/`; the tests link the core alone and rely on this.
@@ -1,5 +1,5 @@
 cmake_minimum_required(VERSION 3.20)
-project(effector VERSION 0.5.2 LANGUAGES CXX)
+project(effector VERSION 0.6.0 LANGUAGES CXX)
 set(CMAKE_CXX_STANDARD 20)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
@@ -40,6 +40,7 @@ add_library(effector_core STATIC
    src/core/registry.cpp
    src/core/rng.cpp
    src/core/style.cpp
    src/core/video.cpp
    src/effects/bitcrush.cpp
    src/effects/blur.cpp
    src/effects/channelsplit.cpp
@@ -70,6 +71,9 @@ add_library(effector_gui STATIC
 )
 target_link_libraries(effector_gui PUBLIC effector_core PkgConfig::GTKMM)
 target_compile_options(effector_gui PRIVATE -Wall -Wextra -Wpedantic)
 # Where a build that was never installed finds its own icon (see app.cpp).
 target_compile_definitions(effector_gui PRIVATE
    EFFECTOR_SOURCE_ICON_DIR="${CMAKE_CURRENT_SOURCE_DIR}/data/icons")
 # --- application --------------------------------------------------------------
 add_executable(effector src/main.cpp)
@@ -79,6 +83,8 @@ target_compile_options(effector PRIVATE -Wall -Wextra -Wpedantic)
 install(TARGETS effector RUNTIME DESTINATION bin)
 # The launcher entry, so the interface shows up in the desktop's app menu.
 install(FILES data/org.effector.Effector.desktop DESTINATION share/applications)
 # The icon it names, in full colour and as a one-colour symbolic for panels.
 install(DIRECTORY data/icons/hicolor DESTINATION share/icons)
 # --- tests --------------------------------------------------------------------
 include(CTest)
@@ -9,6 +9,8 @@ those declarations, so a new effect needs no UI or CLI code.
 Requirements: a C++20 compiler (GCC 13+), CMake 3.20+, `gtkmm-4.0` and
 `gdk-pixbuf-2.0` development packages. On Arch: `gcc cmake ninja gtkmm-4.0`.
 Writing videos needs the `ffmpeg` program at run time (on Arch: `ffmpeg`);
 without it everything else works and the video tests are skipped.
 ```bash
 cmake -S . -B build -G Ninja -DCMAKE_BUILD_TYPE=Release
@@ -58,6 +60,32 @@ Custom hands them back, keeping whatever the format last worked out to. A
 format is saved with the project, so an A4 project reopens as A4 rather than as
 the pixels it happened to be.
 ### Video
 A project can be a video clip instead of a still: switch **Video** on under
 Setup and give it a length and a frame rate, or pick a preset that sets the
 canvas too — Instagram story (1080×1920, 15 s), Instagram reel (30 s),
 Instagram feed video, TikTok / YouTube Short, Square loop (6 s) and Full HD
 clip. The preview renders the whole clip first, shrunk to fit in memory, and
 then loops it, with play/pause and a scale to look at any one frame. **Save
 As…** then writes the video at full size through `ffmpeg`, which has to be
 installed: `.mp4`, `.mov` and `.mkv` as H.264, `.webm` as VP9, `.gif` as a
 palette GIF.
 ```bash
 build/effector -o story.mp4 --video-preset instagram-story -e channelsplit --seed 1 photo.jpg
 build/effector -o loop.gif -s 480x480 --duration 3 --fps 15 -e channelsplit photo.jpg
 ```
 `--duration SECONDS` and `--fps N` make any run a video; a preset fills in
 whatever was not given alongside it. Effects that move over time are video
 effects; for now that is **Channel split**, which in a video sways its
 channels, shakes them from frame to frame and rolls a tracking bar down the
 picture, like a worn tape on an old tube. Its motion params only show in a
 video project, and a still renders exactly as before. Every frame starts from
 the same seed, so stages that do not move hold still while one that does
 moves, and a clip renders frame for frame the same again.
 Any option can also be passed when launching the interface; it becomes the
 starting state (images, canvas size, effect settings, seed).
@@ -0,0 +1,52 @@
 <svg xmlns="http://www.w3.org/2000/svg" width="128" height="128" viewBox="0 0 128 128">
  <!-- Effector: an E split into its colour channels, two slices slipped sideways -->
  <defs>
    <linearGradient id="bg" x1="0" y1="0" x2="0" y2="1">
      <stop offset="0" stop-color="#2b2837"/>
      <stop offset="1" stop-color="#15131c"/>
    </linearGradient>
    <clipPath id="face"><rect x="12" y="10" width="104" height="104" rx="24"/></clipPath>
    <clipPath id="band0"><rect x="0" y="20" width="128" height="30"/></clipPath>
    <clipPath id="band1"><rect x="0" y="50" width="128" height="9"/></clipPath>
    <clipPath id="band2"><rect x="0" y="59" width="128" height="15"/></clipPath>
    <clipPath id="band3"><rect x="0" y="74" width="128" height="6"/></clipPath>
    <clipPath id="band4"><rect x="0" y="80" width="128" height="20"/></clipPath>
  </defs>
  <rect x="12" y="16" width="104" height="104" rx="24" fill="#0b0a10"/>
  <g clip-path="url(#face)">
    <rect x="12" y="10" width="104" height="104" fill="url(#bg)"/>
    <g fill="#ffffff" opacity=".05">
      <rect x="12" y="12" width="104" height="1.4"/>
      <rect x="12" y="16" width="104" height="1.4"/>
      <rect x="12" y="20" width="104" height="1.4"/>
      <rect x="12" y="24" width="104" height="1.4"/>
      <rect x="12" y="28" width="104" height="1.4"/>
      <rect x="12" y="32" width="104" height="1.4"/>
      <rect x="12" y="36" width="104" height="1.4"/>
      <rect x="12" y="40" width="104" height="1.4"/>
      <rect x="12" y="44" width="104" height="1.4"/>
      <rect x="12" y="48" width="104" height="1.4"/>
      <rect x="12" y="52" width="104" height="1.4"/>
      <rect x="12" y="56" width="104" height="1.4"/>
      <rect x="12" y="60" width="104" height="1.4"/>
      <rect x="12" y="64" width="104" height="1.4"/>
      <rect x="12" y="68" width="104" height="1.4"/>
      <rect x="12" y="72" width="104" height="1.4"/>
      <rect x="12" y="76" width="104" height="1.4"/>
      <rect x="12" y="80" width="104" height="1.4"/>
      <rect x="12" y="84" width="104" height="1.4"/>
      <rect x="12" y="88" width="104" height="1.4"/>
      <rect x="12" y="92" width="104" height="1.4"/>
      <rect x="12" y="96" width="104" height="1.4"/>
      <rect x="12" y="100" width="104" height="1.4"/>
      <rect x="12" y="104" width="104" height="1.4"/>
      <rect x="12" y="108" width="104" height="1.4"/>
      <rect x="12" y="112" width="104" height="1.4"/>
    </g>
    <g clip-path="url(#band0)"><g transform="translate(0 0)"><g transform="translate(-5 0)"><rect x="40" y="30" width="16" height="62" fill="#00e5ff"/><rect x="40" y="30" width="48" height="14" fill="#00e5ff"/><rect x="40" y="54" width="40" height="13" fill="#00e5ff"/><rect x="40" y="78" width="48" height="14" fill="#00e5ff"/></g><g transform="translate(5 0)"><rect x="40" y="30" width="16" height="62" fill="#ff2e88"/><rect x="40" y="30" width="48" height="14" fill="#ff2e88"/><rect x="40" y="54" width="40" height="13" fill="#ff2e88"/><rect x="40" y="78" width="48" height="14" fill="#ff2e88"/></g><rect x="40" y="30" width="16" height="62" fill="#ffffff"/><rect x="40" y="30" width="48" height="14" fill="#ffffff"/><rect x="40" y="54" width="40" height="13" fill="#ffffff"/><rect x="40" y="78" width="48" height="14" fill="#ffffff"/></g></g>
    <g clip-path="url(#band1)"><g transform="translate(9 0)"><g transform="translate(-5 0)"><rect x="40" y="30" width="16" height="62" fill="#00e5ff"/><rect x="40" y="30" width="48" height="14" fill="#00e5ff"/><rect x="40" y="54" width="40" height="13" fill="#00e5ff"/><rect x="40" y="78" width="48" height="14" fill="#00e5ff"/></g><g transform="translate(5 0)"><rect x="40" y="30" width="16" height="62" fill="#ff2e88"/><rect x="40" y="30" width="48" height="14" fill="#ff2e88"/><rect x="40" y="54" width="40" height="13" fill="#ff2e88"/><rect x="40" y="78" width="48" height="14" fill="#ff2e88"/></g><rect x="40" y="30" width="16" height="62" fill="#ffffff"/><rect x="40" y="30" width="48" height="14" fill="#ffffff"/><rect x="40" y="54" width="40" height="13" fill="#ffffff"/><rect x="40" y="78" width="48" height="14" fill="#ffffff"/></g></g>
    <g clip-path="url(#band2)"><g transform="translate(0 0)"><g transform="translate(-5 0)"><rect x="40" y="30" width="16" height="62" fill="#00e5ff"/><rect x="40" y="30" width="48" height="14" fill="#00e5ff"/><rect x="40" y="54" width="40" height="13" fill="#00e5ff"/><rect x="40" y="78" width="48" height="14" fill="#00e5ff"/></g><g transform="translate(5 0)"><rect x="40" y="30" width="16" height="62" fill="#ff2e88"/><rect x="40" y="30" width="48" height="14" fill="#ff2e88"/><rect x="40" y="54" width="40" height="13" fill="#ff2e88"/><rect x="40" y="78" width="48" height="14" fill="#ff2e88"/></g><rect x="40" y="30" width="16" height="62" fill="#ffffff"/><rect x="40" y="30" width="48" height="14" fill="#ffffff"/><rect x="40" y="54" width="40" height="13" fill="#ffffff"/><rect x="40" y="78" width="48" height="14" fill="#ffffff"/></g></g>
    <g clip-path="url(#band3)"><g transform="translate(-7 0)"><g transform="translate(-5 0)"><rect x="40" y="30" width="16" height="62" fill="#00e5ff"/><rect x="40" y="30" width="48" height="14" fill="#00e5ff"/><rect x="40" y="54" width="40" height="13" fill="#00e5ff"/><rect x="40" y="78" width="48" height="14" fill="#00e5ff"/></g><g transform="translate(5 0)"><rect x="40" y="30" width="16" height="62" fill="#ff2e88"/><rect x="40" y="30" width="48" height="14" fill="#ff2e88"/><rect x="40" y="54" width="40" height="13" fill="#ff2e88"/><rect x="40" y="78" width="48" height="14" fill="#ff2e88"/></g><rect x="40" y="30" width="16" height="62" fill="#ffffff"/><rect x="40" y="30" width="48" height="14" fill="#ffffff"/><rect x="40" y="54" width="40" height="13" fill="#ffffff"/><rect x="40" y="78" width="48" height="14" fill="#ffffff"/></g></g>
    <g clip-path="url(#band4)"><g transform="translate(0 0)"><g transform="translate(-5 0)"><rect x="40" y="30" width="16" height="62" fill="#00e5ff"/><rect x="40" y="30" width="48" height="14" fill="#00e5ff"/><rect x="40" y="54" width="40" height="13" fill="#00e5ff"/><rect x="40" y="78" width="48" height="14" fill="#00e5ff"/></g><g transform="translate(5 0)"><rect x="40" y="30" width="16" height="62" fill="#ff2e88"/><rect x="40" y="30" width="48" height="14" fill="#ff2e88"/><rect x="40" y="54" width="40" height="13" fill="#ff2e88"/><rect x="40" y="78" width="48" height="14" fill="#ff2e88"/></g><rect x="40" y="30" width="16" height="62" fill="#ffffff"/><rect x="40" y="30" width="48" height="14" fill="#ffffff"/><rect x="40" y="54" width="40" height="13" fill="#ffffff"/><rect x="40" y="78" width="48" height="14" fill="#ffffff"/></g></g>
  </g>
 </svg>
@@ -0,0 +1,10 @@
 <svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 16 16">
  <!-- Effector, one colour: the E with its middle slice slipped sideways -->
  <g fill="#2e3436">
    <rect x="3" y="2" width="10" height="3"/>
    <rect x="3" y="5" width="3" height="1.5"/>
    <rect x="5" y="6.5" width="8" height="3"/>
    <rect x="3" y="9.5" width="3" height="1.5"/>
    <rect x="3" y="11" width="10" height="3"/>
  </g>
 </svg>
@@ -4,7 +4,7 @@ Name=Effector
 GenericName=Image Effects
 Comment=Cascade glitch and collage effects over your photographs
 Exec=effector %F
-Icon=applications-graphics
+Icon=org.effector.Effector
 Terminal=false
 Categories=Graphics;2DGraphics;RasterGraphics;GTK;
 MimeType=image/jpeg;image/png;image/webp;image/tiff;image/bmp;
@@ -2,13 +2,14 @@
 # so pkgver must follow the project() line of CMakeLists.txt (the version core
 # test checks it). From this folder: makepkg -si
 pkgname=effector
-pkgver=0.5.2
+pkgver=0.6.0
 pkgrel=1
 pkgdesc='Image effects app: a GTK4 interface and a headless CLI over pluggable effects'
 arch=('x86_64' 'aarch64')
 url='https://git.plan9.uber.space/hans/effector'
 license=('GPL-3.0-or-later')
 depends=('gtkmm-4.0' 'gdk-pixbuf2' 'pango' 'cairo' 'glib2' 'glibc' 'gcc-libs')
 optdepends=('ffmpeg: write video projects')
 makedepends=('cmake' 'ninja' 'git')
 checkdepends=('xorg-server-xvfb')
 source=("$pkgname::git+file://${startdir%/packaging/arch}#tag=v$pkgver")
@@ -55,6 +55,11 @@ std::string requireValue(int argc, char** argv, int& i, const std::string& flag)
 Options parseOptions(int argc, char** argv) {
    Options options;
    // What was given explicitly, so that a --video-preset fills in only the
    // rest, whichever order the flags come in.
    bool sizeGiven = false;
    bool durationGiven = false;
    bool fpsGiven = false;
    for (int i = 1; i < argc; ++i) {
        const std::string arg = argv[i];
@@ -73,6 +78,7 @@ Options parseOptions(int argc, char** argv) {
            options.output = requireValue(argc, argv, i, arg);
        } else if (arg == "-s" || arg == "--size") {
            const std::string value = requireValue(argc, argv, i, arg);
            sizeGiven = true;
            if (!parseSize(value, options.width, options.height)) {
                throw EffectError("invalid size '" + value + "', expected e.g. 1920x1080 with "
                                  "each side between " + std::to_string(kMinCanvasSide) + " and " +
@@ -92,6 +98,41 @@ Options parseOptions(int argc, char** argv) {
                                  std::to_string(kMinDpi) + "-" + std::to_string(kMaxDpi));
            }
            options.dpi = static_cast<int>(dpi);
        } else if (arg == "--duration") {
            const std::string value = requireValue(argc, argv, i, arg);
            double seconds = 0.0;
            try {
                std::size_t used = 0;
                seconds = std::stod(value, &used);
                if (used != value.size()) seconds = 0.0;
            } catch (const std::exception&) {
                seconds = 0.0;
            }
            if (!(seconds >= kMinDuration) || !(seconds <= kMaxDuration)) {
                throw EffectError("invalid duration '" + value + "', expected seconds between " +
                                  formatSeconds(kMinDuration) + " and " +
                                  formatSeconds(kMaxDuration));
            }
            options.video.enabled = true;
            options.video.duration = seconds;
            durationGiven = true;
        } else if (arg == "--fps") {
            const std::string value = requireValue(argc, argv, i, arg);
            long fps = 0;
            if (!parseLong(value, fps) || fps < kMinFps || fps > kMaxFps) {
                throw EffectError("invalid frame rate '" + value + "', expected " +
                                  std::to_string(kMinFps) + "-" + std::to_string(kMaxFps));
            }
            options.video.enabled = true;
            options.video.fps = static_cast<int>(fps);
            fpsGiven = true;
        } else if (arg == "--video-preset") {
            const std::string value = requireValue(argc, argv, i, arg);
            if (videoPresetByKey(value) == nullptr) {
                throw EffectError("unknown video preset '" + value + "', see --help");
            }
            options.video.enabled = true;
            options.video.preset = value;
        } else if (arg == "--disable") {
            const std::string name = requireValue(argc, argv, i, arg);
            effectByName(name);  // validate now, exactly as -e does
@@ -162,6 +203,18 @@ Options parseOptions(int argc, char** argv) {
            options.images.push_back(arg);
        }
    }
    // A preset fills in whatever was not given on its own: the length, the
    // rate and -- unless -s or --format named one -- the canvas. It keeps its
    // name only while the settings still are the preset's.
    if (const auto* preset = videoPresetByKey(options.video.preset)) {
        if (!durationGiven) options.video.duration = preset->seconds;
        if (!fpsGiven) options.video.fps = preset->fps;
        if (options.format.empty() && !sizeGiven) options.format = preset->canvasFormat;
        if (options.video.duration != preset->seconds || options.video.fps != preset->fps ||
            options.format != preset->canvasFormat) {
            options.video.preset.clear();
        }
    }
    // Applied once everything is parsed, so --dpi may come before --format and
    // so a format always wins over an -s given alongside it.
    if (const auto* format = canvasFormatByKey(options.format)) {
@@ -183,6 +236,11 @@ std::string usage(const char* programName) {
        << "      --format NAME     canvas format, overrides --size (see below)\n"
        << "      --dpi N           resolution of a print format, " << kMinDpi << "-" << kMaxDpi
        << " (default: " << kDefaultDpi << ")\n"
        << "      --duration SECS   render a video this long, " << formatSeconds(kMinDuration)
        << " to " << formatSeconds(kMaxDuration) << "\n"
        << "      --fps N           frames per second of a video, " << kMinFps << "-" << kMaxFps
        << " (default: " << kDefaultFps << ")\n"
        << "      --video-preset NAME  a video's canvas and length in one (see below)\n"
        << "      --disable NAME    keep this effect in the chain but skip it\n"
        << "      --seed N          random seed (default: random)\n"
        << "      --list-effects    list available effects and exit\n"
@@ -197,6 +255,15 @@ std::string usage(const char* programName) {
            << (format.print ? " at --dpi" : "") << "\n";
    }
    out << "\nA video is written through ffmpeg, as .mp4, .mov, .mkv, .webm or .gif by the "
           "name given to\n--output.\n";
    out << "\nVideo presets (--video-preset):\n";
    for (const auto& preset : videoPresets()) {
        out << "  " << preset.key;
        if (preset.key.size() < 20) out << std::string(20 - preset.key.size(), ' ');
        out << "  " << preset.label << ", " << videoPresetDetail(preset) << "\n";
    }
    for (const auto& effect : effects()) {
        out << "\n" << effect->title() << " options:\n";
        for (const auto& spec : effect->params()) {
@@ -204,7 +271,8 @@ std::string usage(const char* programName) {
            if (spec.type != ParamSpec::Type::Bool) flag += " VALUE";
            out << "  " << flag;
            if (flag.size() < 20) out << std::string(20 - flag.size(), ' ');
-            out << "  " << (spec.help.empty() ? spec.label : spec.help) << "\n";
+            out << "  " << (spec.help.empty() ? spec.label : spec.help)
                << (spec.videoOnly ? " (video only)" : "") << "\n";
        }
    }
    return out.str();
@@ -8,6 +8,7 @@
 #include "core/canvas.hpp"
 #include "core/chain.hpp"
 #include "core/params.hpp"
 #include "core/video.hpp"
 namespace effector {
@@ -23,6 +24,9 @@ struct Options {
    int height = 1080;
    std::string format;      // a named canvas format, empty for plain pixels
    int dpi = kDefaultDpi;   // only a print format is rendered at a resolution
    // Enabled by --duration, --fps or --video-preset: the output is then a
    // video, and --output has to name one.
    VideoSettings video;
    std::optional<std::uint64_t> seed;
    ParamValues params;              // only the keys the user actually passed
    bool listEffects = false;
@@ -33,6 +33,7 @@ const std::vector<CanvasFormat>& canvasFormats() {
        {"instagram-post", "Instagram post", false, 1080, 1080, 0.0, 0.0},
        {"instagram-portrait", "Instagram portrait", false, 1080, 1350, 0.0, 0.0},
        {"instagram-story", "Instagram story", false, 1080, 1920, 0.0, 0.0},
        {"vertical-hd", "Vertical Full HD", false, 1080, 1920, 0.0, 0.0},
        {"hd", "Full HD", false, 1920, 1080, 0.0, 0.0},
        {"uhd", "4K UHD", false, 3840, 2160, 0.0, 0.0},
        {"a5", "A5", true, 0, 0, 148.0, 210.0},
@@ -1,5 +1,7 @@
 #include "core/chain.hpp"
 #include <algorithm>
 namespace effector {
 std::vector<const ChainStage*> enabledStages(const std::vector<ChainStage>& stages) {
@@ -29,8 +31,10 @@ ParamValues stageValues(const ChainStage& stage, const StyleSet& styles) {
    return values;
 }
-Image renderChain(const std::vector<ChainStage>& stages, const std::vector<Image>& sources,
+namespace {
-                  int width, int height, Rng& rng, const StyleSet& styles) {
+
 // The stages that run, checked: throws for a chain with nothing to render.
 std::vector<const ChainStage*> runningStages(const std::vector<ChainStage>& stages) {
    if (stages.empty()) throw EffectError("The effect chain is empty.");
    for (const auto& stage : stages) {
        if (!stage.effect) throw EffectError("The effect chain has an empty stage.");
@@ -39,27 +43,83 @@ Image renderChain(const std::vector<ChainStage>& stages, const std::vector<Image
    // A disabled stage never reaches the render at all: it is not handed an
    // image and draws nothing from the shared rng, so switching one off gives
    // back exactly the picture the chain made before it was added.
-    const auto running = enabledStages(stages);
+    auto running = enabledStages(stages);
    if (running.empty()) throw EffectError("Every effect in the chain is disabled.");
    return running;
 }
-    Image image;
+// Runs running[first, last) on `image`, which holds the sources' place for
-    for (std::size_t i = 0; i < running.size(); ++i) {
+// the first stage of the chain and the previous stage's output after it.
 Image runStages(const std::vector<const ChainStage*>& running, std::size_t first,
                std::size_t last, const std::vector<Image>& sources, Image image, int width,
                int height, Rng& rng, const StyleSet& styles, const FrameTime& frame) {
    for (std::size_t i = first; i < last; ++i) {
        const auto& stage = *running[i];
        const auto values = stageValues(stage, styles);
        if (i == 0) {
-            image = stage.effect->render(sources, width, height, rng, values);
+            image = stage.effect->renderFrame(sources, width, height, rng, values, frame);
        } else {
            // Feeding the previous result back in as the only source is what
            // cascading means here; effects need to know nothing about it.
            const std::vector<Image> previous = {std::move(image)};
-            image = stage.effect->render(previous, width, height, rng, values);
+            image = stage.effect->renderFrame(previous, width, height, rng, values, frame);
        }
    }
    return image;
 }
 }  // namespace
 Image renderChain(const std::vector<ChainStage>& stages, const std::vector<Image>& sources,
                  int width, int height, Rng& rng, const StyleSet& styles,
                  const FrameTime& frame) {
    const auto running = runningStages(stages);
    return runStages(running, 0, running.size(), sources, Image(), width, height, rng, styles,
                     frame);
 }
 bool chainAnimated(const std::vector<ChainStage>& stages, const StyleSet& styles) {
    for (const auto* stage : enabledStages(stages)) {
        if (stage->effect->animated(stageValues(*stage, styles))) return true;
    }
    return false;
 }
 int renderFrames(const std::vector<ChainStage>& stages, const std::vector<Image>& sources,
                 int width, int height, std::uint64_t seed, const StyleSet& styles,
                 const VideoSettings& video,
                 const std::function<bool(int index, Image&& frame)>& onFrame) {
    const auto running = runningStages(stages);
    const int count = video.frameCount();
    const int fps = std::clamp(video.fps, kMinFps, kMaxFps);
    // Everything before the first stage that moves is the same on every
    // frame -- the same seed, the same values, no time -- so it is rendered
    // once, as frame 0, and picked up from there. The rng is copied along
    // with the picture, which is what makes the shortcut exact.
    std::size_t still = 0;
    while (still < running.size() &&
           !running[still]->effect->animated(stageValues(*running[still], styles))) {
        ++still;
    }
    Rng prefixRng(seed);
    const Image prefix = runStages(running, 0, still, sources, Image(), width, height, prefixRng,
                                   styles, FrameTime{0, count, fps});
    for (int index = 0; index < count; ++index) {
        const FrameTime frame{index, count, fps};
        Rng rng = prefixRng;
        Image image = still == running.size()
                          ? prefix
                          : runStages(running, still, running.size(), sources, prefix, width,
                                      height, rng, styles, frame);
        if (!onFrame(index, std::move(image))) return index + 1;
    }
    return count;
 }
 bool chainNeedsSources(const std::vector<ChainStage>& stages) {
    const auto running = enabledStages(stages);
    if (running.empty()) return false;
@@ -1,5 +1,6 @@
 #pragma once
 #include <functional>
 #include <string>
 #include <vector>
@@ -8,6 +9,7 @@
 #include "core/params.hpp"
 #include "core/rng.hpp"
 #include "core/style.hpp"
 #include "core/video.hpp"
 namespace effector {
@@ -52,8 +54,28 @@ std::vector<const ChainStage*> enabledStages(const std::vector<ChainStage>& stag
 // reproduces the cascade byte for byte. Throws when no stage is left to run.
 // `styles` is the project's pool; a chain built without one -- the command
 // line's -- passes none and renders from the stages alone.
 //
 // `frame` says where in a video the render sits, a still by default; every
 // stage is handed it, and only one that moves makes anything of it.
 Image renderChain(const std::vector<ChainStage>& stages, const std::vector<Image>& sources,
-                  int width, int height, Rng& rng, const StyleSet& styles = {});
+                  int width, int height, Rng& rng, const StyleSet& styles = {},
                  const FrameTime& frame = {});
 // Whether any stage that runs moves over time with the values it runs with.
 bool chainAnimated(const std::vector<ChainStage>& stages, const StyleSet& styles = {});
 // Renders every frame of a video, in order, handing each to `onFrame`; it
 // returning false stops the render there. Frame k is exactly what
 // renderChain gives with a fresh Rng(seed) and FrameTime{k, count, fps} --
 // every frame starts from the same seed, so a stage that does not move
 // renders the same picture throughout rather than reshuffling on every
 // frame. The stages before the first one that moves are rendered once, and
 // their picture and the rng state they leave are reused for every frame.
 // Returns the number of frames handed out.
 int renderFrames(const std::vector<ChainStage>& stages, const std::vector<Image>& sources,
                 int width, int height, std::uint64_t seed, const StyleSet& styles,
                 const VideoSettings& video,
                 const std::function<bool(int index, Image&& frame)>& onFrame);
 // Whether the chain has to be given source images. Only the first stage that
 // runs ever sees them — every later one works on the stage before it — so this
@@ -16,6 +16,19 @@ public:
    using std::runtime_error::runtime_error;
 };
 // Where a render sits in time. The default -- no frame rate -- is a still
 // picture; a video hands every frame its index, the clip's length in frames
 // and its rate, so an effect that moves works out where it is from these
 // alone and a frame can be rendered on its own, in any order.
 struct FrameTime {
    int index = 0;
    int count = 1;
    int fps = 0;
    bool video() const noexcept { return fps > 0; }
    double seconds() const noexcept { return video() ? static_cast<double>(index) / fps : 0.0; }
 };
 // Base class for every effect. Canvas size and the random source are common to
 // all of them; params() covers only the effect-specific knobs.
 class Effect {
@@ -45,9 +58,27 @@ public:
        return title();
    }
    // Whether a stage with these values changes from one frame of a video to
    // the next. A stage that does not is rendered once for the whole clip.
    virtual bool animated(const ParamValues& values) const {
        (void)values;
        return false;
    }
    virtual Image render(const std::vector<Image>& sources, int width, int height, Rng& rng,
                         const ParamValues& values) const = 0;
    // One frame of a video, or a still when `frame` says so. An effect that
    // does not move needs only render(), which this falls back to. One that
    // does must leave `rng` in the same state on every frame -- a frame's own
    // randomness comes from a generator of its own -- so the stages after it
    // stay put while it moves.
    virtual Image renderFrame(const std::vector<Image>& sources, int width, int height, Rng& rng,
                              const ParamValues& values, const FrameTime& frame) const {
        (void)frame;
        return render(sources, width, height, rng, values);
    }
    ParamValues defaults() const;
 };
@@ -91,6 +91,39 @@ Image Image::load(const std::string& path, std::vector<std::uint8_t>* alphaOut)
    return image;
 }
 Image Image::scaledToFit(int maxSide) const {
    const int longest = std::max(width_, height_);
    if (empty() || maxSide < 1 || longest <= maxSide) return *this;
    const double scale = static_cast<double>(maxSide) / longest;
    const int outWidth = std::max(1, static_cast<int>(width_ * scale));
    const int outHeight = std::max(1, static_cast<int>(height_ * scale));
    Image out(outWidth, outHeight);
    for (int y = 0; y < outHeight; ++y) {
        const int y0 = static_cast<int>(static_cast<long>(y) * height_ / outHeight);
        const int y1 = std::max(y0 + 1, static_cast<int>(static_cast<long>(y + 1) * height_ / outHeight));
        std::uint8_t* target = out.row(y);
        for (int x = 0; x < outWidth; ++x) {
            const int x0 = static_cast<int>(static_cast<long>(x) * width_ / outWidth);
            const int x1 = std::max(x0 + 1, static_cast<int>(static_cast<long>(x + 1) * width_ / outWidth));
            unsigned sum[3] = {0, 0, 0};
            for (int sy = y0; sy < y1; ++sy) {
                const std::uint8_t* in = row(sy) + static_cast<std::size_t>(x0) * 3;
                for (int sx = x0; sx < x1; ++sx, in += 3) {
                    sum[0] += in[0];
                    sum[1] += in[1];
                    sum[2] += in[2];
                }
            }
            const unsigned area = static_cast<unsigned>((y1 - y0) * (x1 - x0));
            for (int c = 0; c < 3; ++c) {
                target[static_cast<std::size_t>(x) * 3 + c] = static_cast<std::uint8_t>(sum[c] / area);
            }
        }
    }
    return out;
 }
 void Image::save(const std::string& path) const {
    if (empty()) throw std::runtime_error("nothing to save");
@@ -40,6 +40,11 @@ public:
    // which is what an effect compositing the image needs.
    static Image load(const std::string& path, std::vector<std::uint8_t>* alphaOut = nullptr);
    // A copy shrunk so that its longer side is at most `maxSide`, each pixel
    // the average of the ones it covers; an image already that small comes
    // back as it is. For previews: nothing rendered goes through it.
    Image scaledToFit(int maxSide) const;
    // Encodes by file extension; png is used when the extension is unknown.
    void save(const std::string& path) const;
@@ -16,6 +16,12 @@ ParamSpec ParamSpec::styled() const {
    return copy;
 }
 ParamSpec ParamSpec::forVideo() const {
    ParamSpec copy = *this;
    copy.videoOnly = true;
    return copy;
 }
 ParamSpec ParamSpec::makeInt(std::string key, std::string label, long defaultValue, long minimum,
                             long maximum, std::string help, long step) {
    ParamSpec spec;
@@ -27,6 +27,10 @@ struct ParamSpec {
    // Whether a named style carries this param rather than the stage it sits
    // on: see core/style.hpp.
    bool inStyle = false;
    // Whether the param only means something in a video project -- how a
    // stage moves over time. The interface leaves it out of a still project,
    // where it would change nothing.
    bool videoOnly = false;
    std::string flag() const;  // "strip_height" -> "--strip-height"
@@ -34,6 +38,9 @@ struct ParamSpec {
    // reads makeDouble("font_size", ...).styled() and the factories keep the
    // signatures they have.
    ParamSpec styled() const;
    // A copy of this spec marked as mattering only in a video project, read
    // the same way: makeInt("split_jitter", ...).forVideo().
    ParamSpec forVideo() const;
    static ParamSpec makeInt(std::string key, std::string label, long defaultValue, long minimum,
                             long maximum, std::string help = {}, long step = 1);
@@ -319,6 +319,25 @@ int canvasDpi(const Json& value) {
    return static_cast<int>(value.number);
 }
 // A clip's length in seconds and its frame rate, checked like the canvas.
 double videoDuration(const Json& value) {
    if (value.kind != Json::Kind::Number || !(value.number >= kMinDuration) ||
        !(value.number <= kMaxDuration)) {
        throw EffectError("the video duration must be between " + formatSeconds(kMinDuration) +
                          " and " + formatSeconds(kMaxDuration));
    }
    return value.number;
 }
 int videoFps(const Json& value) {
    if (value.kind != Json::Kind::Number || value.number != std::trunc(value.number) ||
        !(value.number >= kMinFps) || !(value.number <= kMaxFps)) {
        throw EffectError("the video frame rate must be a whole number between " +
                          std::to_string(kMinFps) + " and " + std::to_string(kMaxFps));
    }
    return static_cast<int>(value.number);
 }
 std::string resolve(const std::string& path, const std::string& directory) {
    std::filesystem::path file(path);
    if (file.is_absolute() || directory.empty()) return path;
@@ -435,6 +454,16 @@ std::string projectToJson(const Project& project, const std::string& directory)
        if (format->print) out << ", \"dpi\": " << project.dpi;
    }
    out << "},\n";
    // Only a video says anything about time: a still project reads exactly as
    // it did before there were videos.
    if (project.video.enabled) {
        out << "  \"video\": {\"duration\": " << number(project.video.duration, 3)
            << ", \"fps\": " << project.video.fps;
        if (const auto* preset = videoPresetByKey(project.video.preset)) {
            out << ", \"preset\": " << quote(preset->key);
        }
        out << "},\n";
    }
    if (project.seed) out << "  \"seed\": " << *project.seed << ",\n";
    out << "  \"sources\": [";
@@ -506,6 +535,21 @@ Project projectFromJson(const std::string& text, const std::string& directory) {
        }
    }
    if (const auto* video = root.member("video"); video != nullptr &&
                                                  video->kind == Json::Kind::Object) {
        project.video.enabled = true;
        if (const auto* duration = video->member("duration")) {
            project.video.duration = videoDuration(*duration);
        }
        if (const auto* fps = video->member("fps")) project.video.fps = videoFps(*fps);
        // Like a canvas format, a preset this build does not know is just the
        // user's own settings: the numbers were written too.
        if (const auto* name = video->member("preset"); name != nullptr &&
                                                        name->kind == Json::Kind::String) {
            if (const auto* preset = videoPresetByKey(name->text)) project.video.preset = preset->key;
        }
    }
    if (const auto* seed = root.member("seed")) {
        // Taken from the digits rather than from the double: a 64-bit seed has
        // more bits than a double has mantissa, and a seed that comes back off
@@ -9,6 +9,7 @@
 #include "core/chain.hpp"
 #include "core/params.hpp"
 #include "core/style.hpp"
 #include "core/video.hpp"
 namespace effector {
@@ -30,6 +31,8 @@ struct Project {
    // resolution for.
    std::string format;
    int dpi = kDefaultDpi;
    // Whether the project is a video, and how long and how fast.
    VideoSettings video;
    std::optional<std::uint64_t> seed;
 };
@@ -0,0 +1,272 @@
 #include "core/video.hpp"
 #include <fcntl.h>
 #include <signal.h>
 #include <spawn.h>
 #include <sys/wait.h>
 #include <unistd.h>
 #include <algorithm>
 #include <cerrno>
 #include <cmath>
 #include <cstdlib>
 #include <cstring>
 #include <filesystem>
 #include <locale>
 #include <mutex>
 #include <sstream>
 #include "core/canvas.hpp"
 #include "core/effect.hpp"
 extern char** environ;
 namespace effector {
 int VideoSettings::frameCount() const {
    const double seconds = std::clamp(duration, kMinDuration, kMaxDuration);
    const int rate = std::clamp(fps, kMinFps, kMaxFps);
    return std::max(1, static_cast<int>(std::lround(seconds * rate)));
 }
 const std::vector<VideoPreset>& videoPresets() {
    // A story segment runs fifteen seconds, a reel is best kept to half a
    // minute, and a loop is short enough to watch go round a few times.
    static const std::vector<VideoPreset> presets = {
        {"instagram-story", "Instagram story", "instagram-story", 15.0, 30},
        {"instagram-reel", "Instagram reel", "instagram-story", 30.0, 30},
        {"instagram-feed", "Instagram feed video", "instagram-portrait", 10.0, 30},
        {"vertical-short", "TikTok / YouTube Short", "vertical-hd", 30.0, 30},
        {"square-loop", "Square loop", "instagram-post", 6.0, 30},
        {"hd-clip", "Full HD clip", "hd", 10.0, 30},
    };
    return presets;
 }
 const VideoPreset* videoPresetByKey(const std::string& key) {
    if (key.empty()) return nullptr;
    for (const auto& preset : videoPresets()) {
        if (preset.key == key) return &preset;
    }
    return nullptr;
 }
 // In the C locale whatever the user's is, for the same reason as the
 // millimetres of a paper size: "7.5 s", never "7,5 s".
 std::string formatSeconds(double seconds) {
    std::ostringstream out;
    out.imbue(std::locale::classic());
    out.setf(std::ios::fixed);
    out.precision(1);
    out << seconds;
    std::string text = out.str();
    if (text.size() > 2 && text.compare(text.size() - 2, 2, ".0") == 0) text.resize(text.size() - 2);
    return text + " s";
 }
 std::string videoPresetDetail(const VideoPreset& preset) {
    const auto* format = canvasFormatByKey(preset.canvasFormat);
    std::string text = format != nullptr ? canvasFormatDetail(*format) + " · " : std::string();
    return text + formatSeconds(preset.seconds);
 }
 namespace {
 std::string lowerExtension(const std::string& path) {
    std::string extension = std::filesystem::path(path).extension().string();
    std::transform(extension.begin(), extension.end(), extension.begin(),
                   [](unsigned char c) { return static_cast<char>(std::tolower(c)); });
    return extension;
 }
 // The container ffmpeg is told to write, by extension; empty for one that
 // is not a video.
 std::string muxerFor(const std::string& extension) {
    if (extension == ".mp4") return "mp4";
    if (extension == ".mov") return "mov";
    if (extension == ".mkv") return "matroska";
    if (extension == ".webm") return "webm";
    if (extension == ".gif") return "gif";
    return {};
 }
 }  // namespace
 bool isVideoPath(const std::string& path) { return !muxerFor(lowerExtension(path)).empty(); }
 bool ffmpegAvailable() {
    const char* path = std::getenv("PATH");
    if (path == nullptr) return false;
    std::stringstream dirs(path);
    std::string dir;
    while (std::getline(dirs, dir, ':')) {
        if (dir.empty()) dir = ".";
        if (::access((dir + "/ffmpeg").c_str(), X_OK) == 0) return true;
    }
    return false;
 }
 VideoWriter::VideoWriter(const std::string& path, int width, int height, int fps)
    : path_(path), width_(width), height_(height) {
    const std::string muxer = muxerFor(lowerExtension(path));
    if (muxer.empty()) {
        throw EffectError("A video is written as .mp4, .mov, .mkv, .webm or .gif, not '" +
                          std::filesystem::path(path).filename().string() + "'.");
    }
    if (width < 1 || height < 1) throw EffectError("Canvas size must be at least 1x1 pixels.");
    // A write to an ffmpeg that has already died must come back as an error
    // to report, not as a signal that takes the whole program down with it.
    static std::once_flag ignorePipe;
    std::call_once(ignorePipe, [] { ::signal(SIGPIPE, SIG_IGN); });
    std::vector<std::string> args = {
        "ffmpeg", "-hide_banner", "-loglevel", "error", "-y",
        "-f", "rawvideo", "-pix_fmt", "rgb24",
        "-s", std::to_string(width) + "x" + std::to_string(height),
        "-r", std::to_string(std::clamp(fps, kMinFps, kMaxFps)),
        "-i", "pipe:0", "-an",
    };
    if (muxer == "gif") {
        // One palette made for the whole clip, rather than the fixed web one.
        args.insert(args.end(), {"-vf", "split[a][b];[b]palettegen[p];[a][p]paletteuse",
                                 "-loop", "0"});
    } else {
        // 4:2:0 wants even sides; a pixel of padding beats refusing the canvas.
        args.insert(args.end(), {"-vf", "pad=ceil(iw/2)*2:ceil(ih/2)*2"});
        if (muxer == "webm") {
            args.insert(args.end(), {"-c:v", "libvpx-vp9", "-crf", "32", "-b:v", "0",
                                     "-row-mt", "1"});
        } else {
            args.insert(args.end(), {"-c:v", "libx264", "-preset", "medium", "-crf", "18"});
        }
        args.insert(args.end(), {"-pix_fmt", "yuv420p"});
        if (muxer == "mp4" || muxer == "mov") args.insert(args.end(), {"-movflags", "+faststart"});
    }
    // "file:" keeps a name that starts with a dash, or holds a colon, a file.
    args.insert(args.end(), {"-f", muxer, "file:" + path});
    int pipeEnds[2] = {-1, -1};
    if (::pipe2(pipeEnds, O_CLOEXEC) != 0) {
        throw EffectError(std::string("Could not start ffmpeg: ") + std::strerror(errno));
    }
    errors_ = std::tmpfile();
    if (errors_ != nullptr) ::fcntl(fileno(errors_), F_SETFD, FD_CLOEXEC);
    posix_spawn_file_actions_t actions;
    posix_spawn_file_actions_init(&actions);
    posix_spawn_file_actions_adddup2(&actions, pipeEnds[0], STDIN_FILENO);
    if (errors_ != nullptr) posix_spawn_file_actions_adddup2(&actions, fileno(errors_), STDERR_FILENO);
    std::vector<char*> argv;
    for (auto& arg : args) argv.push_back(arg.data());
    argv.push_back(nullptr);
    pid_t child = -1;
    const int spawned = ::posix_spawnp(&child, "ffmpeg", &actions, nullptr, argv.data(), environ);
    posix_spawn_file_actions_destroy(&actions);
    ::close(pipeEnds[0]);
    if (spawned != 0) {
        ::close(pipeEnds[1]);
        if (errors_ != nullptr) std::fclose(errors_);
        errors_ = nullptr;
        if (spawned == ENOENT) {
            throw EffectError("Writing a video needs ffmpeg, which is not installed or not on "
                              "the PATH.");
        }
        throw EffectError(std::string("Could not start ffmpeg: ") + std::strerror(spawned));
    }
    child_ = child;
    input_ = pipeEnds[1];
 }
 VideoWriter::~VideoWriter() {
    if (child_ > 0) cancel();
    if (errors_ != nullptr) std::fclose(errors_);
 }
 void VideoWriter::write(const Image& frame) {
    if (input_ < 0) throw EffectError("The video has already been closed.");
    if (frame.width() != width_ || frame.height() != height_) {
        throw EffectError("Every frame of a video must be the same size.");
    }
    const std::uint8_t* data = frame.data();
    std::size_t left = frame.byteSize();
    while (left > 0) {
        const ssize_t written = ::write(input_, data, left);
        if (written < 0) {
            if (errno == EINTR) continue;
            failed("ffmpeg stopped taking frames");
        }
        data += written;
        left -= static_cast<std::size_t>(written);
    }
 }
 int VideoWriter::wait() {
    int status = 0;
    while (::waitpid(child_, &status, 0) < 0) {
        if (errno != EINTR) {
            status = -1;
            break;
        }
    }
    child_ = -1;
    return status;
 }
 void VideoWriter::finish() {
    if (child_ <= 0) return;
    ::close(input_);
    input_ = -1;
    const int status = wait();
    if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
        std::error_code ignored;
        std::filesystem::remove(path_, ignored);
        std::string message = "ffmpeg could not write the video";
        const std::string said = errorOutput();
        if (!said.empty()) message += ": " + said;
        throw EffectError(message);
    }
 }
 void VideoWriter::cancel() {
    if (input_ >= 0) {
        ::close(input_);
        input_ = -1;
    }
    if (child_ > 0) {
        // Not SIGTERM: ffmpeg takes that as "finish up", and flushing a slow
        // encoder can take many seconds for a file that is thrown away.
        ::kill(child_, SIGKILL);
        wait();
    }
    std::error_code ignored;
    std::filesystem::remove(path_, ignored);
 }
 void VideoWriter::failed(const std::string& what) {
    cancel();
    std::string message = what;
    const std::string said = errorOutput();
    if (!said.empty()) message += ": " + said;
    throw EffectError(message);
 }
 // The last thing ffmpeg said, which is where it names the problem.
 std::string VideoWriter::errorOutput() const {
    if (errors_ == nullptr) return {};
    std::string text;
    std::rewind(errors_);
    char buffer[4096];
    std::size_t read = 0;
    while ((read = std::fread(buffer, 1, sizeof buffer, errors_)) > 0) text.append(buffer, read);
    while (!text.empty() && (text.back() == '\n' || text.back() == '\r' || text.back() == ' ')) {
        text.pop_back();
    }
    const auto lastLine = text.rfind('\n');
    if (lastLine != std::string::npos) text.erase(0, lastLine + 1);
    return text;
 }
 }  // namespace effector
@@ -0,0 +1,104 @@
 #pragma once
 #include <sys/types.h>
 #include <cstdio>
 #include <string>
 #include <vector>
 #include "core/image.hpp"
 namespace effector {
 // The frame rates and lengths both front-ends accept. Five minutes at sixty
 // frames is 18000 frames -- already a long wait -- and a tenth of a second is
 // the shortest clip that still has a few frames in it.
 inline constexpr int kMinFps = 1;
 inline constexpr int kMaxFps = 60;
 inline constexpr int kDefaultFps = 30;
 inline constexpr double kMinDuration = 0.1;
 inline constexpr double kMaxDuration = 300.0;
 inline constexpr double kDefaultDuration = 10.0;
 // Whether a project is a video, and how long and how fast. A still project
 // carries the other fields too, so switching video off and on again gives
 // the same clip back.
 struct VideoSettings {
    bool enabled = false;
    double duration = kDefaultDuration;  // seconds
    int fps = kDefaultFps;
    // The preset the settings came from, empty for the user's own. Like a
    // canvas format it is the presentation of the numbers, never the truth:
    // the render goes by duration and fps.
    std::string preset;
    // The frames the clip has: the length at the rate, never fewer than one.
    int frameCount() const;
 };
 // A named kind of clip both front-ends offer: a canvas and a length that go
 // together, so "Instagram story" is one choice rather than three.
 struct VideoPreset {
    std::string key;           // written in a project and given to --video-preset
    std::string label;         // shown in the interface
    std::string canvasFormat;  // a key of canvasFormats()
    double seconds = 0.0;
    int fps = kDefaultFps;
 };
 // In the order they are offered.
 const std::vector<VideoPreset>& videoPresets();
 // Null when the key names no preset -- an empty or unknown key is "custom".
 const VideoPreset* videoPresetByKey(const std::string& key);
 // "1080 × 1920 px · 15 s", for the dropdown and for --help.
 std::string videoPresetDetail(const VideoPreset& preset);
 // "15 s", "7.5 s": a length as the interface and --help show it.
 std::string formatSeconds(double seconds);
 // Whether a file name asks for a video: .mp4, .mov, .mkv, .webm or .gif.
 bool isVideoPath(const std::string& path);
 // Whether an `ffmpeg` the writer below can run is on the PATH.
 bool ffmpegAvailable();
 // Encodes frames into a video file by piping them, raw, into the `ffmpeg`
 // program. Run as a plain argv rather than through a shell, so a file name is
 // never read as anything but a file name. The container and codec follow the
 // extension: H.264 for .mp4, .mov and .mkv, VP9 for .webm, a palette GIF for
 // .gif. The encoded bytes are ffmpeg's business; the frames going in are the
 // ones the seed decides.
 //
 // Throws EffectError when ffmpeg is missing, fails, or quits early, with what
 // it had to say. A writer that is neither finished nor cancelled cancels
 // itself on destruction, so a half-written file is never left behind.
 class VideoWriter {
 public:
    VideoWriter(const std::string& path, int width, int height, int fps);
    ~VideoWriter();
    VideoWriter(const VideoWriter&) = delete;
    VideoWriter& operator=(const VideoWriter&) = delete;
    // Every frame must be the size the writer was opened with.
    void write(const Image& frame);
    // Closes the stream, waits for ffmpeg and throws if it failed.
    void finish();
    // Stops ffmpeg and removes the unfinished file.
    void cancel();
 private:
    void failed(const std::string& what);  // cancels, then throws with ffmpeg's words
    std::string errorOutput() const;
    int wait();
    std::string path_;
    int width_ = 0;
    int height_ = 0;
    pid_t child_ = -1;
    int input_ = -1;           // the write end of ffmpeg's stdin
    std::FILE* errors_ = nullptr;  // ffmpeg's stderr, read back on failure
 };
 }  // namespace effector
@@ -2,6 +2,8 @@
 #include <algorithm>
 #include <array>
 #include <cmath>
 #include <numbers>
 #include <vector>
 #include "core/parallel.hpp"
@@ -22,6 +24,26 @@ const std::vector<ParamSpec>& ChannelSplitEffect::params() const {
                              "rgb moves all three channels apart; red_cyan moves red one way and "
                              "green and blue the other, as 3D glasses would; random moves one "
                              "channel picked at random."),
        ParamSpec::makeInt("split_wobble", "Wobble", 4, 0, 256,
                           "How far in pixels the channels sway back and forth over time.")
            .forVideo(),
        ParamSpec::makeDouble("split_wobble_speed", "Wobble speed", 0.5, 0.0, 10.0,
                              "Sways per second, rounded so that the clip loops without a jump.",
                              0.1, 1)
            .forVideo(),
        ParamSpec::makeInt("split_jitter", "Jitter", 2, 0, 256,
                           "Furthest in pixels the channels shake, anew on every frame and, in "
                           "per_band mode, for every band.")
            .forVideo(),
        ParamSpec::makeInt("split_roll", "Tracking bar", 16, 0, 512,
                           "How far in pixels a bar rolling down the picture tears the rows "
                           "sideways and the channels apart; 0 for none.")
            .forVideo(),
        ParamSpec::makeDouble("split_roll_time", "Bar pass", 4.0, 0.5, 60.0,
                              "Seconds the tracking bar takes from top to bottom, rounded so "
                              "that the clip loops without a jump.",
                              0.5, 1)
            .forVideo(),
    };
    return specs;
 }
@@ -35,28 +57,68 @@ struct Offset {
 using ChannelOffsets = std::array<Offset, 3>;
-ChannelOffsets drawOffsets(Rng& rng, int amount, const std::string& channels) {
+ChannelOffsets drawOffsets(Rng& rng, int amount, const std::string& channels, int& moved) {
    ChannelOffsets offsets{};
    auto draw = [&] {
        return Offset{static_cast<int>(rng.inRange(-amount, amount)),
                      static_cast<int>(rng.inRange(-amount, amount))};
    };
    moved = -1;
    if (channels == "red_cyan") {
        const Offset red = draw();
        offsets[0] = red;
        offsets[1] = offsets[2] = Offset{-red.dx, -red.dy};
    } else if (channels == "random") {
-        offsets[rng.below(2)] = draw();
+        moved = static_cast<int>(rng.below(2));
        offsets[static_cast<std::size_t>(moved)] = draw();
    } else {
        for (auto& offset : offsets) offset = draw();
    }
    return offsets;
 }
-}  // namespace
+// A motion of each channel, handed out the way the mode moves channels: all
 // three on their own, green and blue opposite red, or only the one channel
 // that was picked -- so the motion never moves a channel the still left alone.
 using Motion = std::array<double, 3>;
-Image ChannelSplitEffect::render(const std::vector<Image>& sources, int width, int height, Rng& rng,
+Motion spread(const Motion& motion, const std::string& channels, int moved) {
-                                 const ParamValues& values) const {
+    if (channels == "red_cyan") return {motion[0], -motion[0], -motion[0]};
    if (moved >= 0) {
        Motion only{};
        only[static_cast<std::size_t>(moved)] = motion[0];
        return only;
    }
    return motion;
 }
 double unit(Rng& rng) { return static_cast<double>(rng.next() >> 11) * 0x1.0p-53; }
 struct MotionSettings {
    int wobble = 0;
    double wobbleSpeed = 0.0;
    int jitter = 0;
    int roll = 0;
    double rollTime = 1.0;
    explicit MotionSettings(const ParamValues& values)
        : wobble(static_cast<int>(std::max(0L, paramInt(values, "split_wobble", 4)))),
          wobbleSpeed(std::max(0.0, paramDouble(values, "split_wobble_speed", 0.5))),
          jitter(static_cast<int>(std::max(0L, paramInt(values, "split_jitter", 2)))),
          roll(static_cast<int>(std::max(0L, paramInt(values, "split_roll", 16)))),
          rollTime(std::max(0.5, paramDouble(values, "split_roll_time", 4.0))) {}
    bool moves() const { return (wobble > 0 && wobbleSpeed > 0.0) || jitter > 0 || roll > 0; }
 };
 // Rounds a rate so a whole number of cycles fits the clip, never fewer than
 // one: the last frame then leads straight back into the first.
 double loopRate(double perSecond, double clipSeconds) {
    return std::max(1.0, std::round(perSecond * clipSeconds)) / clipSeconds;
 }
 Image renderSplit(const std::vector<Image>& sources, int width, int height, Rng& rng,
                  const ParamValues& values, const FrameTime& frame) {
    if (width < 1 || height < 1) throw EffectError("Canvas size must be at least 1x1 pixels.");
    const int amount = static_cast<int>(std::max(0L, paramInt(values, "split_amount", 12)));
@@ -71,20 +133,105 @@ Image ChannelSplitEffect::render(const std::vector<Image>& sources, int width, i
    const int band = perBand ? bandHeight : height;
    const int bandCount = (height + band - 1) / band;
    std::vector<ChannelOffsets> plan;
    std::vector<int> moved;
    plan.reserve(static_cast<std::size_t>(bandCount));
-    for (int i = 0; i < bandCount; ++i) plan.push_back(drawOffsets(rng, amount, channels));
+    moved.reserve(static_cast<std::size_t>(bandCount));
    for (int i = 0; i < bandCount; ++i) {
        int only = -1;
        plan.push_back(drawOffsets(rng, amount, channels, only));
        moved.push_back(only);
    }
    // Every row's offsets, and a sideways shift of the whole row. A still is
    // just the band plan; a frame of a video adds the motion to it.
    std::vector<ChannelOffsets> rows(static_cast<std::size_t>(height));
    std::vector<int> shift(static_cast<std::size_t>(height), 0);
    for (int y = 0; y < height; ++y) rows[static_cast<std::size_t>(y)] = plan[static_cast<std::size_t>(y / band)];
    const MotionSettings motion(values);
    if (frame.video() && motion.moves()) {
        // The same draws on every frame, after the still's: where each
        // channel starts its sway and which way it sways. The shake is the
        // one thing that differs between frames, so it comes from a generator
        // of the frame's own, seeded by one more draw -- the shared rng leaves
        // every frame in the same state, and the stages after this one hold
        // still while it moves.
        std::array<double, 3> phase{};
        std::array<double, 3> angle{};
        for (int c = 0; c < 3; ++c) {
            phase[static_cast<std::size_t>(c)] = unit(rng) * 2.0 * std::numbers::pi;
            angle[static_cast<std::size_t>(c)] = unit(rng) * 2.0 * std::numbers::pi;
        }
        Rng shake(rng.next() ^ (0x9e3779b97f4a7c15ULL * static_cast<std::uint64_t>(frame.index + 1)));
        const double clip = static_cast<double>(std::max(1, frame.count)) / frame.fps;
        const double t = frame.seconds();
        Motion swayX{};
        Motion swayY{};
        if (motion.wobble > 0 && motion.wobbleSpeed > 0.0) {
            const double rate = loopRate(motion.wobbleSpeed, clip);
            for (std::size_t c = 0; c < 3; ++c) {
                const double sway = motion.wobble * std::sin(2.0 * std::numbers::pi * rate * t + phase[c]);
                swayX[c] = sway * std::cos(angle[c]);
                swayY[c] = sway * std::sin(angle[c]);
            }
        }
        // The tracking bar: an eighth of the picture, soft at both edges,
        // entering above the top and leaving below the bottom.
        const double barHeight = std::max(8.0, height / 8.0);
        const double passes = loopRate(1.0 / motion.rollTime, clip);
        const double along = std::fmod(t * passes, 1.0);
        const double barTop = -barHeight + along * (height + barHeight);
        for (int b = 0; b < bandCount; ++b) {
            Motion jitterX{};
            Motion jitterY{};
            if (motion.jitter > 0) {
                for (std::size_t c = 0; c < 3; ++c) {
                    jitterX[c] = static_cast<double>(shake.inRange(-motion.jitter, motion.jitter));
                    // Mostly sideways, as a picture losing its horizontal hold.
                    jitterY[c] = static_cast<double>(shake.inRange(-motion.jitter, motion.jitter)) / 3.0;
                }
            }
            const int only = moved[static_cast<std::size_t>(b)];
            const Motion dx = spread({swayX[0] + jitterX[0], swayX[1] + jitterX[1], swayX[2] + jitterX[2]},
                                     channels, only);
            const Motion dy = spread({swayY[0] + jitterY[0], swayY[1] + jitterY[1], swayY[2] + jitterY[2]},
                                     channels, only);
            // The bar pulls red one way and blue the other (or the moved
            // channel alone), whatever the sway is doing.
            const Motion apart = spread({1.0, 0.0, -1.0}, channels, only);
            const int end = std::min(height, (b + 1) * band);
            for (int y = b * band; y < end; ++y) {
                double bar = 0.0;
                if (motion.roll > 0 && y >= barTop && y < barTop + barHeight) {
                    bar = motion.roll * std::sin(std::numbers::pi * (y - barTop) / barHeight);
                }
                auto& offsets = rows[static_cast<std::size_t>(y)];
                for (std::size_t c = 0; c < 3; ++c) {
                    offsets[c].dx += static_cast<int>(std::lround(dx[c] + bar * apart[c]));
                    offsets[c].dy += static_cast<int>(std::lround(dy[c]));
                }
                shift[static_cast<std::size_t>(y)] = static_cast<int>(std::lround(bar / 2.0));
            }
        }
    }
    Image canvas(width, height);
    parallelFor(static_cast<std::size_t>(height), [&](std::size_t begin, std::size_t end) {
        for (std::size_t y = begin; y < end; ++y) {
-            const ChannelOffsets& offsets = plan[y / static_cast<std::size_t>(band)];
+            const ChannelOffsets& offsets = rows[y];
            std::uint8_t* out = canvas.row(static_cast<int>(y));
            for (int c = 0; c < 3; ++c) {
                const Offset& offset = offsets[static_cast<std::size_t>(c)];
                const int dx = offset.dx + shift[y];
                const int sy = std::clamp(static_cast<int>(y) - offset.dy, 0, height - 1);
                const std::uint8_t* in = input.row(sy);
                for (int x = 0; x < width; ++x) {
-                    const int sx = std::clamp(x - offset.dx, 0, width - 1);
+                    const int sx = std::clamp(x - dx, 0, width - 1);
                    out[static_cast<std::size_t>(x) * 3 + c] = in[static_cast<std::size_t>(sx) * 3 + c];
                }
            }
@@ -94,4 +241,21 @@ Image ChannelSplitEffect::render(const std::vector<Image>& sources, int width, i
    return canvas;
 }
 }  // namespace
 bool ChannelSplitEffect::animated(const ParamValues& values) const {
    return MotionSettings(values).moves();
 }
 Image ChannelSplitEffect::render(const std::vector<Image>& sources, int width, int height, Rng& rng,
                                 const ParamValues& values) const {
    return renderSplit(sources, width, height, rng, values, FrameTime{});
 }
 Image ChannelSplitEffect::renderFrame(const std::vector<Image>& sources, int width, int height,
                                      Rng& rng, const ParamValues& values,
                                      const FrameTime& frame) const {
    return renderSplit(sources, width, height, rng, values, frame);
 }
 }  // namespace effector
@@ -6,6 +6,9 @@ namespace effector {
 // Knocks the red, green and blue planes out of register, either the whole image
 // at once or band by band, each band with offsets of its own.
 // In a video the channels do not sit still: they sway, shake from frame to
 // frame, and a tracking bar rolls down the picture as on a worn tape or an old
 // tube. A still picture is rendered exactly as it always was.
 // A pure transform: it needs no source images, and leading a chain with
 // sources loaded it starts from a crop of a randomly chosen one.
 class ChannelSplitEffect : public Effect {
@@ -18,9 +21,12 @@ public:
    }
    const std::vector<ParamSpec>& params() const override;
    bool needsSources() const override { return false; }
    bool animated(const ParamValues& values) const override;
    Image render(const std::vector<Image>& sources, int width, int height, Rng& rng,
                 const ParamValues& values) const override;
    Image renderFrame(const std::vector<Image>& sources, int width, int height, Rng& rng,
                      const ParamValues& values, const FrameTime& frame) const override;
 };
 }  // namespace effector
@@ -13,6 +13,14 @@ int runGui(const Options& initial, int argc, char** argv) {
    auto app = Gtk::Application::create("org.effector.Effector",
                                        Gio::Application::Flags::NON_UNIQUE);
    app->signal_startup().connect([] {
        // An installed Effector finds its icon in the hicolor theme; one run
        // straight from the build tree falls back to the copy in the sources.
        const char* icon = "org.effector.Effector";
        auto theme = Gtk::IconTheme::get_for_display(Gdk::Display::get_default());
        if (!theme->has_icon(icon)) theme->add_search_path(EFFECTOR_SOURCE_ICON_DIR);
        Gtk::Window::set_default_icon_name(icon);
    });
    return app->make_window_and_run<EffectorWindow>(0, nullptr, initial);
 }
@@ -14,6 +14,7 @@
 #include "core/registry.hpp"
 #include "core/rng.hpp"
 #include "core/version.hpp"
 #include "core/video.hpp"
 namespace effector {
 namespace {
@@ -42,6 +43,20 @@ Glib::RefPtr<Gdk::Texture> toTexture(const Image& image) {
                                      bytes, image.stride());
 }
 // The most memory a preview clip may take, all frames together. The frames
 // are shrunk to fit, so a long clip is previewed smaller rather than not at
 // all; the longer side stays between the two bounds below.
 constexpr double kClipBudgetBytes = 256.0 * 1024 * 1024;
 constexpr int kClipMinSide = 160;
 constexpr int kClipMaxSide = 720;
 int clipSide(int width, int height, int frames) {
    const double full = 3.0 * width * height * std::max(1, frames);
    const double scale = std::min(1.0, std::sqrt(kClipBudgetBytes / full));
    const int side = static_cast<int>(std::max(width, height) * scale);
    return std::clamp(side, kClipMinSide, kClipMaxSide);
 }
 Gtk::Label* sectionLabel(const char* text) {
    auto* label = Gtk::make_managed<Gtk::Label>(text);
    label->set_xalign(0.0F);
@@ -97,6 +112,9 @@ EffectorWindow::EffectorWindow(const Options& initial) {
    renderDone_.connect(sigc::mem_fun(*this, &EffectorWindow::onRenderFinished));
    loadProgress_.connect(sigc::mem_fun(*this, &EffectorWindow::onLoadProgress));
    loadFinished_.connect(sigc::mem_fun(*this, &EffectorWindow::onLoadFinished));
    clipProgress_.connect(sigc::mem_fun(*this, &EffectorWindow::onClipProgress));
    exportProgress_.connect(sigc::mem_fun(*this, &EffectorWindow::onExportProgress));
    exportDone_.connect(sigc::mem_fun(*this, &EffectorWindow::onExportFinished));
    buildUi();
    applyInitial(initial);
@@ -116,9 +134,13 @@ EffectorWindow::~EffectorWindow() {
    chainSplitFit_.disconnect();
    recentChanged_.disconnect();
    loadWindowDelay_.disconnect();
    playTimer_.disconnect();
    loadCancel_.store(true, std::memory_order_relaxed);
    renderCancel_.store(true, std::memory_order_relaxed);
    exportCancel_.store(true, std::memory_order_relaxed);
    if (loader_.joinable()) loader_.join();
    if (worker_.joinable()) worker_.join();
    if (exporter_.joinable()) exporter_.join();  // cancelled: removes its half-written file
 }
 // ------------------------------------------------------------------- UI ---
@@ -334,6 +356,8 @@ Gtk::Widget& EffectorWindow::buildSetupTab() {
    updateSourcesLabel();
    tab->append(sourcesSection_);
    tab->append(buildVideoSection());
    tab->append(*sectionLabel("Canvas"));
    tab->append(buildCanvasSection());
@@ -392,6 +416,8 @@ Gtk::Widget& EffectorWindow::buildCanvasSection() {
    widthSpin_.set_range(kMinCanvasSide, kMaxCanvasSide);
    widthSpin_.set_increments(1, 100);
    widthSpin_.set_value(1920);
    widthSpin_.set_name("canvas-width");
    heightSpin_.set_name("canvas-height");
    heightSpin_.set_range(kMinCanvasSide, kMaxCanvasSide);
    heightSpin_.set_increments(1, 100);
    heightSpin_.set_value(1080);
@@ -484,6 +510,220 @@ void EffectorWindow::syncCanvasWidgets() {
    if (!quiet) onParamChanged();
 }
 // ---------------------------------------------------------------- video ---
 // A still project shows only the switch; a video shows its preset, length and
 // rate below it. The preset list reads like the canvas one: "Custom" first,
 // then every preset with what it amounts to.
 Gtk::Widget& EffectorWindow::buildVideoSection() {
    auto* box = Gtk::make_managed<Gtk::Box>(Gtk::Orientation::VERTICAL, 6);
    auto* heading = Gtk::make_managed<Gtk::Box>(Gtk::Orientation::HORIZONTAL, 8);
    auto* label = sectionLabel("Video");
    label->set_hexpand(true);
    heading->append(*label);
    videoSwitch_.set_name("video");
    videoSwitch_.set_valign(Gtk::Align::CENTER);
    videoSwitch_.set_tooltip_text("Make a video clip rather than a still picture");
    videoSwitch_.property_active().signal_changed().connect(
        sigc::mem_fun(*this, &EffectorWindow::onVideoToggled));
    heading->append(videoSwitch_);
    box->append(*heading);
    videoDetails_.set_orientation(Gtk::Orientation::VERTICAL);
    videoDetails_.set_spacing(6);
    // Index 0 is "Custom"; every later index is videoPresets()[index - 1].
    std::vector<Glib::ustring> labels{"Custom"};
    for (const auto& preset : videoPresets()) {
        labels.push_back(preset.label + " (" + videoPresetDetail(preset) + ")");
    }
    videoPresetDrop_.set_name("video-preset");
    videoPresetDrop_.set_model(Gtk::StringList::create(labels));
    videoPresetDrop_.set_selected(0);
    videoPresetDrop_.set_tooltip_text("A canvas and a length made for one place a clip is shown");
    videoPresetDrop_.property_selected().signal_changed().connect(
        sigc::mem_fun(*this, &EffectorWindow::onVideoPresetSelected));
    videoDetails_.append(videoPresetDrop_);
    auto* grid = Gtk::make_managed<Gtk::Grid>();
    grid->set_column_spacing(8);
    grid->set_row_spacing(6);
    durationSpin_.set_name("video-duration");
    durationSpin_.set_range(kMinDuration, kMaxDuration);
    durationSpin_.set_increments(0.5, 5.0);
    durationSpin_.set_digits(1);
    durationSpin_.set_value(kDefaultDuration);
    fpsSpin_.set_name("video-fps");
    fpsSpin_.set_range(kMinFps, kMaxFps);
    fpsSpin_.set_increments(1, 5);
    fpsSpin_.set_value(kDefaultFps);
    for (auto* spin : {&durationSpin_, &fpsSpin_}) {
        spin->set_hexpand(true);
        scrollPastUnlessFocused(*spin);
        spin->signal_value_changed().connect(
            sigc::mem_fun(*this, &EffectorWindow::onVideoTimingChanged));
    }
    auto* durationLabel = Gtk::make_managed<Gtk::Label>("Length (s)");
    durationLabel->set_xalign(0.0F);
    auto* fpsLabel = Gtk::make_managed<Gtk::Label>("Frames/s");
    fpsLabel->set_xalign(0.0F);
    grid->attach(*durationLabel, 0, 0);
    grid->attach(durationSpin_, 1, 0);
    grid->attach(*fpsLabel, 0, 1);
    grid->attach(fpsSpin_, 1, 1);
    videoDetails_.append(*grid);
    videoDetails_.set_visible(false);
    box->append(videoDetails_);
    return *box;
 }
 VideoSettings EffectorWindow::videoSettings() const {
    VideoSettings video;
    video.enabled = isVideo();
    video.duration = durationSpin_.get_value();
    video.fps = static_cast<int>(fpsSpin_.get_value());
    const auto selected = videoPresetDrop_.get_selected();
    const auto& presets = videoPresets();
    if (selected != GTK_INVALID_LIST_POSITION && selected > 0 && selected <= presets.size()) {
        video.preset = presets[selected - 1].key;
    }
    return video;
 }
 void EffectorWindow::setVideoSettings(const VideoSettings& video) {
    const bool suspended = suspendVideoSync_;
    suspendVideoSync_ = true;
    durationSpin_.set_value(video.duration);
    fpsSpin_.set_value(video.fps);
    guint selected = 0;
    const auto& presets = videoPresets();
    for (std::size_t i = 0; i < presets.size(); ++i) {
        if (presets[i].key == video.preset) selected = static_cast<guint>(i + 1);
    }
    videoPresetDrop_.set_selected(selected);
    videoSwitch_.set_active(video.enabled);
    videoDetails_.set_visible(video.enabled);
    suspendVideoSync_ = suspended;
    playbackBar_.set_visible(false);
    clearClip();
    buildParamWidgets();  // the motion params come and go with the switch
 }
 void EffectorWindow::onVideoToggled() {
    videoDetails_.set_visible(isVideo());
    if (suspendVideoSync_) return;
    // What was on screen was the other kind of result, and cannot be saved as
    // this one.
    result_ = Image();
    clearClip();
    saveButton_.set_sensitive(false);
    buildParamWidgets();
    requestRender();
 }
 // A preset decides the canvas too, so picking one fills in the format as well
 // as the timing -- one render for all of it.
 void EffectorWindow::onVideoPresetSelected() {
    if (suspendVideoSync_) return;
    const auto* preset = videoPresetByKey(videoSettings().preset);
    if (preset == nullptr) return;  // "Custom": leave the numbers as they are
    suspendVideoSync_ = true;
    durationSpin_.set_value(preset->seconds);
    fpsSpin_.set_value(preset->fps);
    setCanvasFormat(preset->canvasFormat, static_cast<int>(dpiSpin_.get_value()));
    suspendVideoSync_ = false;
    requestRender();
 }
 void EffectorWindow::onVideoTimingChanged() {
    if (suspendVideoSync_) return;
    matchVideoPreset();
    requestRender();
 }
 void EffectorWindow::matchVideoPreset() {
    if (suspendVideoSync_) return;
    const auto* preset = videoPresetByKey(videoSettings().preset);
    if (preset == nullptr) return;
    const bool same = std::abs(durationSpin_.get_value() - preset->seconds) < 1e-9 &&
                      static_cast<int>(fpsSpin_.get_value()) == preset->fps &&
                      canvasFormatKey() == preset->canvasFormat;
    if (same) return;
    suspendVideoSync_ = true;
    videoPresetDrop_.set_selected(0);
    suspendVideoSync_ = false;
 }
 // Frames come over from the worker a few at a time and are turned into
 // textures here, on the main thread. The clip on screen keeps playing until
 // the new one is complete; the very first one shows its frames as they come.
 void EffectorWindow::onClipProgress() {
    std::vector<Image> frames;
    {
        std::lock_guard<std::mutex> lock(resultMutex_);
        frames.swap(pendingFrames_);
    }
    if (!renderingVideo_) return;  // left over from a render that was dropped
    for (const auto& frame : frames) incomingClip_.push_back(toTexture(frame));
    if (frames.empty()) return;
    if (clip_.empty()) {
        picture_.set_paintable(incomingClip_.back());
        previewStack_.set_visible_child("picture");
    }
    status_.set_text("Rendering preview · frame " + std::to_string(incomingClip_.size()) + " of " +
                     std::to_string(incomingTotal_));
 }
 void EffectorWindow::showClipFrame(int index) {
    if (clip_.empty()) return;
    playFrame_ = std::clamp(index, 0, static_cast<int>(clip_.size()) - 1);
    picture_.set_paintable(clip_[static_cast<std::size_t>(playFrame_)]);
    suspendScrub_ = true;
    playbackScale_.set_value(playFrame_);
    suspendScrub_ = false;
    playbackTime_.set_text(formatSeconds(static_cast<double>(playFrame_) / clipFps_) + " / " +
                           formatSeconds(static_cast<double>(clip_.size()) / clipFps_));
 }
 void EffectorWindow::startPlayback() {
    playTimer_.disconnect();
    if (clip_.empty()) return;
    playbackScale_.set_range(0, std::max(1, static_cast<int>(clip_.size()) - 1));
    playbackBar_.set_visible(true);
    showClipFrame(playFrame_);
    if (!playing_) return;
    playTimer_ = Glib::signal_timeout().connect(
        [this] {
            showClipFrame((playFrame_ + 1) % static_cast<int>(clip_.size()));
            return true;
        },
        static_cast<unsigned>(std::max(1, 1000 / std::max(1, clipFps_))));
 }
 void EffectorWindow::stopPlayback() { playTimer_.disconnect(); }
 void EffectorWindow::setPlaying(bool playing) {
    playing_ = playing;
    playButton_.set_icon_name(playing ? "media-playback-pause-symbolic"
                                      : "media-playback-start-symbolic");
    playButton_.set_tooltip_text(playing ? "Pause" : "Play");
    if (playing) {
        startPlayback();
    } else {
        stopPlayback();
    }
 }
 void EffectorWindow::clearClip() {
    stopPlayback();
    clip_.clear();
    incomingClip_.clear();
    playFrame_ = 0;
    playbackBar_.set_visible(false);
 }
 Gtk::Widget& EffectorWindow::buildPreview() {
    picture_.set_can_shrink(true);
    picture_.set_content_fit(Gtk::ContentFit::CONTAIN);
@@ -516,6 +756,37 @@ Gtk::Widget& EffectorWindow::buildPreview() {
    status_.set_margin_top(6);
    status_.set_margin_bottom(8);
    status_.add_css_class("dim-label");
    // Play and pause, and a scale to look at any one frame; only a video has it.
    playbackBar_.set_name("playback");
    playbackBar_.set_orientation(Gtk::Orientation::HORIZONTAL);
    playbackBar_.set_spacing(8);
    playbackBar_.set_margin_start(8);
    playbackBar_.set_margin_end(8);
    playbackBar_.set_margin_top(6);
    playButton_.set_icon_name("media-playback-pause-symbolic");
    playButton_.set_tooltip_text("Pause");
    playButton_.signal_clicked().connect([this] { setPlaying(!playing_); });
    playbackBar_.append(playButton_);
    playbackScale_.set_orientation(Gtk::Orientation::HORIZONTAL);
    playbackScale_.set_hexpand(true);
    playbackScale_.set_draw_value(false);
    playbackScale_.set_range(0, 1);
    playbackScale_.set_increments(1, 10);
    playbackScale_.set_tooltip_text("Drag to look at one frame");
    playbackScale_.signal_value_changed().connect([this] {
        if (suspendScrub_) return;
        // Looking at a frame means holding it: playback stops there.
        if (playing_) setPlaying(false);
        showClipFrame(static_cast<int>(std::lround(playbackScale_.get_value())));
    });
    playbackBar_.append(playbackScale_);
    playbackTime_.add_css_class("dim-label");
    playbackTime_.add_css_class("numeric");
    playbackBar_.append(playbackTime_);
    playbackBar_.set_visible(false);
    box->append(playbackBar_);
    box->append(status_);
    return *box;
 }
@@ -557,6 +828,9 @@ void EffectorWindow::buildParamWidgets() {
    }
    for (const auto& spec : stage.effect->params()) {
        // How a stage moves means nothing in a still, so it is left out there;
        // the values stay with the stage for when the project becomes a video.
        if (spec.videoOnly && !isVideo()) continue;
        // A styled param is read from the style while one is followed, so the
        // widgets show what the stage will actually render with.
        const bool shared = style != nullptr && spec.inStyle;
@@ -1011,6 +1285,7 @@ void EffectorWindow::applyInitial(const Options& initial) {
    widthSpin_.set_value(initial.width);
    heightSpin_.set_value(initial.height);
    setCanvasFormat(initial.format, initial.dpi);  // a format fills the spins itself
    setVideoSettings(initial.video);
    if (initial.seed) {
        seed_ = *initial.seed;
        seedEntry_.set_text(std::to_string(seed_));
@@ -1689,6 +1964,7 @@ void EffectorWindow::onParamChanged() {
    // styled one can rename every stage sharing the style.
    for (std::size_t i = 0; i < stageLabels_.size() && i < stages_.size(); ++i)
        stageLabels_[i]->set_text(stageLabel(i));
    matchVideoPreset();  // the canvas may have left the preset's format
    requestRender();
 }
@@ -1758,6 +2034,7 @@ std::string EffectorWindow::missingText() const {
 void EffectorWindow::showPlaceholder() {
    result_ = Image();
    clearClip();
    saveButton_.set_sensitive(false);
    placeholder_.set_text(missingText());
    previewStack_.set_visible_child("placeholder");
@@ -1786,9 +2063,13 @@ void EffectorWindow::startRender() {
    if (!canRender()) return;
    if (rendering_) {
        staleResult_ = true;  // a fresh render follows this one
        // A clip takes seconds; there is no point finishing one whose
        // settings are already out of date.
        renderCancel_.store(true, std::memory_order_relaxed);
        return;
    }
    rendering_ = true;
    renderCancel_.store(false, std::memory_order_relaxed);
    const auto sources = sources_;
    const auto stages = stages_;  // a snapshot, like the sources
@@ -1796,17 +2077,46 @@ void EffectorWindow::startRender() {
    const int width = static_cast<int>(widthSpin_.get_value());
    const int height = static_cast<int>(heightSpin_.get_value());
    const std::uint64_t seed = seed_;
    const VideoSettings video = videoSettings();
    spinner_.start();
    recreateButton_.set_sensitive(false);
-    worker_ = std::thread([this, sources, stages, styles, width, height, seed] {
+    renderingVideo_ = video.enabled;
    if (video.enabled) {
        {
            std::lock_guard<std::mutex> lock(resultMutex_);
            pendingFrames_.clear();
        }
        incomingClip_.clear();
        incomingTotal_ = video.frameCount();
        status_.set_text("Rendering preview…");
    }
    worker_ = std::thread([this, sources, stages, styles, width, height, seed, video] {
        Image image;
        std::string error;
        const auto start = std::chrono::steady_clock::now();
        try {
            if (video.enabled) {
                // Rendered at the full size, so the preview shows what the
                // file will hold, and shrunk only to be kept.
                const int side = clipSide(width, height, video.frameCount());
                renderFrames(stages, *sources, width, height, seed, styles, video,
                             [this, side](int, Image&& frame) {
                                 if (renderCancel_.load(std::memory_order_relaxed)) return false;
                                 Image small = frame.scaledToFit(side);
                                 {
                                     std::lock_guard<std::mutex> lock(resultMutex_);
                                     pendingFrames_.push_back(std::move(small));
                                 }
                                 clipProgress_.emit();
                                 return true;
                             });
            } else {
                Rng rng(seed);
                image = renderChain(stages, *sources, width, height, rng, styles);
            }
        } catch (const std::exception& exception) {
            error = exception.what();
        }
@@ -1826,6 +2136,9 @@ void EffectorWindow::startRender() {
 void EffectorWindow::onRenderFinished() {
    if (worker_.joinable()) worker_.join();
    rendering_ = false;
    onClipProgress();  // whatever frames came in after the last wake-up
    const bool wasVideo = renderingVideo_;
    renderingVideo_ = false;
    Image image;
    std::string error;
@@ -1839,6 +2152,7 @@ void EffectorWindow::onRenderFinished() {
    if (staleResult_) {  // settings changed while this one was running
        staleResult_ = false;
        incomingClip_.clear();
        startRender();
        return;
    }
@@ -1848,25 +2162,45 @@ void EffectorWindow::onRenderFinished() {
    if (!error.empty()) {
        result_ = Image();
        clearClip();
        saveButton_.set_sensitive(false);
        showError(error);
        return;
    }
    clearError();
    std::ostringstream status;
    status.setf(std::ios::fixed);
    status.precision(1);
    const std::size_t effects = enabledStages(stages_).size();
    if (wasVideo) {
        result_ = Image();
        clip_ = std::move(incomingClip_);
        incomingClip_.clear();
        clipFps_ = videoSettings().fps;
        if (playFrame_ >= static_cast<int>(clip_.size())) playFrame_ = 0;
        previewStack_.set_visible_child("picture");
        saveButton_.set_sensitive(!clip_.empty());
        startPlayback();
        status << clip_.size() << " frames · " << effects << (effects == 1 ? " effect" : " effects")
               << " · " << millis / 1000.0 << " s";
    } else {
        clearClip();
        result_ = std::move(image);
        picture_.set_paintable(toTexture(result_));
        previewStack_.set_visible_child("picture");
        saveButton_.set_sensitive(true);
        status << effects << (effects == 1 ? " effect" : " effects") << " · " << millis << " ms";
    }
    // The line itself stays short; the full chain and setup go in the tooltip.
    const std::size_t effects = enabledStages(stages_).size();
    std::ostringstream status;
    status.setf(std::ios::fixed);
    status.precision(1);
    status << effects << (effects == 1 ? " effect" : " effects") << " · " << millis << " ms";
    std::ostringstream details;
-    details << chainTitle(stages_) << " · " << result_.width() << "×" << result_.height() << " · ";
+    details << chainTitle(stages_) << " · " << static_cast<int>(widthSpin_.get_value()) << "×"
            << static_cast<int>(heightSpin_.get_value()) << " · ";
    if (wasVideo) {
        const auto video = videoSettings();
        details << formatSeconds(video.duration) << " at " << video.fps << " fps · ";
    }
    if (!sources_->empty()) {
        details << sources_->size() << (sources_->size() == 1 ? " source" : " sources") << " · ";
    }
@@ -1945,6 +2279,7 @@ Project EffectorWindow::currentProject() const {
    project.height = static_cast<int>(heightSpin_.get_value());
    project.format = canvasFormatKey();
    project.dpi = static_cast<int>(dpiSpin_.get_value());
    project.video = videoSettings();
    project.seed = seed_;
    return project;
 }
@@ -1965,6 +2300,7 @@ void EffectorWindow::applyProject(const Project& project, const std::string& pat
    widthSpin_.set_value(project.width);
    heightSpin_.set_value(project.height);
    setCanvasFormat(project.format, project.dpi);
    setVideoSettings(project.video);
    seed_ = project.seed.value_or(Rng::randomSeed());
    seedEntry_.set_text(std::to_string(seed_));
@@ -1988,6 +2324,7 @@ void EffectorWindow::clearSources() {
    if (loading_) dropLoadedImages_ = true;
    result_ = Image();
    clearClip();
    saveButton_.set_sensitive(false);
    previewStack_.set_visible_child("placeholder");
 }
@@ -2220,7 +2557,7 @@ void EffectorWindow::showAbout() {
        aboutDialog_->set_program_name("Effector");
        aboutDialog_->set_version(std::string(kVersion));
        aboutDialog_->set_comments("Image effects, cascaded through a chain.");
-        aboutDialog_->set_logo_icon_name("applications-graphics");
+        aboutDialog_->set_logo_icon_name("org.effector.Effector");
        aboutDialog_->set_copyright("Copyright © 2026 Si");
        aboutDialog_->set_license_type(Gtk::License::GPL_3_0);
    }
@@ -2287,11 +2624,13 @@ void EffectorWindow::updateTitle() {
 // --------------------------------------------------------------- saving ---
 void EffectorWindow::onSave() {
-    if (result_.empty()) return;
+    const bool video = isVideo();
    if (video ? clip_.empty() || exporting_ : result_.empty()) return;
    auto dialog = Gtk::FileDialog::create();
-    dialog->set_title("Save image");
+    dialog->set_title(video ? "Save video" : "Save image");
-    dialog->set_initial_name("effector-" + chainSlug(stages_) + "-" + std::to_string(seed_) + ".png");
+    dialog->set_initial_name("effector-" + chainSlug(stages_) + "-" + std::to_string(seed_) +
                             (video ? ".mp4" : ".png"));
    dialog->save(*this, [this, dialog](const Glib::RefPtr<Gio::AsyncResult>& result) {
        onSaveChosen(result, dialog);
    });
@@ -2307,8 +2646,19 @@ void EffectorWindow::onSaveChosen(const Glib::RefPtr<Gio::AsyncResult>& result,
    } catch (const Glib::Error&) {
        return;  // cancelled
    }
    if (path.extension().empty()) path.replace_extension(".png");
    if (isVideo()) {
        if (path.extension().empty()) path.replace_extension(".mp4");
        if (!isVideoPath(path.string())) {
            showError("A video is saved as .mp4, .mov, .mkv, .webm or .gif, not " +
                      path.filename().string() + ".");
            return;
        }
        startExport(path.string());
        return;
    }
    if (path.extension().empty()) path.replace_extension(".png");
    try {
        result_.save(path.string());
    } catch (const std::exception& error) {
@@ -2320,6 +2670,138 @@ void EffectorWindow::onSaveChosen(const Glib::RefPtr<Gio::AsyncResult>& result,
    status_.set_tooltip_text("Saved " + path.string());
 }
 // The preview keeps only small frames, so the file is rendered again at the
 // full size, frame by frame, straight into ffmpeg. That takes a while, which
 // is why it has a window of its own and can be cancelled.
 void EffectorWindow::startExport(const std::string& path) {
    if (exporting_) return;
    if (exporter_.joinable()) exporter_.join();
    exporting_ = true;
    exportCancel_.store(false, std::memory_order_relaxed);
    exportFrames_.store(0, std::memory_order_relaxed);
    exportPath_ = path;
    exportError_.clear();
    saveButton_.set_sensitive(false);
    const auto sources = sources_;
    const auto stages = stages_;
    const auto styles = styles_;
    const int width = static_cast<int>(widthSpin_.get_value());
    const int height = static_cast<int>(heightSpin_.get_value());
    const std::uint64_t seed = seed_;
    const VideoSettings video = videoSettings();
    exportTotal_ = video.frameCount();
    exportWindow_ = std::make_unique<Gtk::Window>();
    exportWindow_->set_name("export");
    exportWindow_->set_title("Saving video");
    exportWindow_->set_transient_for(*this);
    exportWindow_->set_modal(true);
    exportWindow_->set_resizable(false);
    exportWindow_->set_default_size(420, -1);
    auto* box = Gtk::make_managed<Gtk::Box>(Gtk::Orientation::VERTICAL, 12);
    box->set_margin(18);
    auto* heading = Gtk::make_managed<Gtk::Label>("Saving " +
                                                  std::filesystem::path(path).filename().string());
    heading->set_xalign(0.0F);
    heading->set_ellipsize(Pango::EllipsizeMode::MIDDLE);
    heading->add_css_class("heading");
    box->append(*heading);
    auto* bar = Gtk::make_managed<Gtk::ProgressBar>();
    bar->set_show_text(true);
    bar->set_text("frame 0 of " + std::to_string(exportTotal_));
    box->append(*bar);
    exportBar_ = bar;
    auto* cancel = Gtk::make_managed<Gtk::Button>("Cancel");
    cancel->set_halign(Gtk::Align::END);
    cancel->signal_clicked().connect(sigc::mem_fun(*this, &EffectorWindow::cancelExport));
    box->append(*cancel);
    // As with reading images: closing means Cancel, and the window stays up
    // until the exporter has actually stopped and cleaned up.
    exportWindow_->signal_close_request().connect(
        [this] {
            cancelExport();
            return true;
        },
        false);
    exportWindow_->set_child(*box);
    exportWindow_->present();
    exporter_ = std::thread([this, path, sources, stages, styles, width, height, seed, video] {
        std::string error;
        try {
            VideoWriter writer(path, width, height, video.fps);
            renderFrames(stages, *sources, width, height, seed, styles, video,
                         [this, &writer](int, Image&& frame) {
                             if (exportCancel_.load(std::memory_order_relaxed)) return false;
                             writer.write(frame);
                             exportFrames_.fetch_add(1, std::memory_order_relaxed);
                             exportProgress_.emit();
                             return true;
                         });
            if (exportCancel_.load(std::memory_order_relaxed)) {
                writer.cancel();
            } else {
                writer.finish();
            }
        } catch (const std::exception& exception) {
            error = exception.what();
        }
        {
            std::lock_guard<std::mutex> lock(resultMutex_);
            exportError_ = std::move(error);
        }
        exportDone_.emit();
    });
 }
 void EffectorWindow::onExportProgress() {
    if (exportBar_ == nullptr || exportCancel_.load(std::memory_order_relaxed)) return;
    const int done = exportFrames_.load(std::memory_order_relaxed);
    exportBar_->set_fraction(exportTotal_ > 0 ? static_cast<double>(done) / exportTotal_ : 0.0);
    exportBar_->set_text("frame " + std::to_string(done) + " of " + std::to_string(exportTotal_));
 }
 void EffectorWindow::onExportFinished() {
    if (exporter_.joinable()) exporter_.join();
    exporting_ = false;
    closeExportWindow();
    saveButton_.set_sensitive(isVideo() ? !clip_.empty() : !result_.empty());
    std::string error;
    {
        std::lock_guard<std::mutex> lock(resultMutex_);
        error = exportError_;
    }
    if (!error.empty()) {
        showError("Could not save the video: " + error);
        return;
    }
    if (exportCancel_.load(std::memory_order_relaxed)) {
        status_.set_text("Saving cancelled");
        status_.set_tooltip_text("");
        return;
    }
    clearError();
    status_.set_text("Saved " + exportPath_);
    status_.set_tooltip_text("Saved " + exportPath_);
 }
 void EffectorWindow::cancelExport() {
    if (!exporting_) return;
    exportCancel_.store(true, std::memory_order_relaxed);
    if (exportBar_ != nullptr) exportBar_->set_text("Cancelling…");
 }
 void EffectorWindow::closeExportWindow() {
    exportBar_ = nullptr;
    if (!exportWindow_) return;
    exportWindow_->set_hide_on_close(false);
    exportWindow_->hide();
    exportWindow_.reset();
 }
 // --------------------------------------------------------------- errors ---
 void EffectorWindow::showError(const std::string& message) {
@@ -18,6 +18,7 @@
 #include "core/image.hpp"
 #include "core/project.hpp"
 #include "core/style.hpp"
 #include "core/video.hpp"
 namespace effector {
@@ -87,6 +88,34 @@ private:
    void syncCanvasWidgets();
    void removeSource(Gtk::ListBoxRow* row);
    // Video: a switch that makes the project a clip, and its length, rate and
    // preset. A preset owns the canvas format as well as the timing; changing
    // any of them by hand drops it back to "Custom".
    Gtk::Widget& buildVideoSection();
    VideoSettings videoSettings() const;
    void setVideoSettings(const VideoSettings& video);  // quietly, for a project
    void onVideoToggled();
    void onVideoPresetSelected();
    void onVideoTimingChanged();
    void matchVideoPreset();  // "Custom" once the settings are no longer the preset's
    bool isVideo() const { return videoSwitch_.get_active(); }
    // The preview of a video is the whole clip, rendered first and then looped.
    void onClipProgress();   // dispatcher: frames arrived from the worker
    void showClipFrame(int index);
    void startPlayback();
    void stopPlayback();
    void setPlaying(bool playing);
    void clearClip();
    // Writing a video file: rendered again at full size, on a thread of its
    // own, into ffmpeg, with a progress window that can cancel it.
    void startExport(const std::string& path);
    void onExportProgress();
    void onExportFinished();
    void cancelExport();
    void closeExportWindow();
    Gtk::Widget& buildChainSection();
    Gtk::Widget& buildAddMenu();      // the menu of effects that can be appended
    void appendStage(const EffectPtr& effect);
@@ -205,6 +234,35 @@ private:
    Image pendingImage_;
    std::string pendingError_;
    double pendingMillis_ = 0.0;
    // Set to stop a clip render early once its settings are out of date.
    std::atomic<bool> renderCancel_{false};
    bool renderingVideo_ = false;  // what the render in flight is making
    // The clip being previewed: small frames, ready to show, and the frames
    // of the clip being rendered, which take its place once it is complete.
    Glib::Dispatcher clipProgress_;
    std::vector<Image> pendingFrames_;  // handed over under resultMutex_
    std::vector<Glib::RefPtr<Gdk::Texture>> clip_;
    std::vector<Glib::RefPtr<Gdk::Texture>> incomingClip_;
    int incomingTotal_ = 0;
    int clipFps_ = kDefaultFps;
    int playFrame_ = 0;
    bool playing_ = true;
    sigc::connection playTimer_;
    bool suspendScrub_ = false;  // set while playback moves the scale itself
    // Video export
    std::thread exporter_;
    Glib::Dispatcher exportProgress_;
    Glib::Dispatcher exportDone_;
    std::atomic<bool> exportCancel_{false};
    std::atomic<int> exportFrames_{0};
    int exportTotal_ = 0;
    bool exporting_ = false;
    std::string exportPath_;
    std::string exportError_;  // written by the exporter before exportDone_
    std::unique_ptr<Gtk::Window> exportWindow_;
    Gtk::ProgressBar* exportBar_ = nullptr;  // nulled with the window
    // Widgets
    Gtk::Label banner_;
@@ -224,6 +282,12 @@ private:
    Gtk::SpinButton heightSpin_;
    Gtk::SpinButton dpiSpin_;
    Gtk::Label* dpiLabel_ = nullptr;  // hidden along with the dpi spin
    Gtk::Switch videoSwitch_;
    Gtk::Box videoDetails_;  // hidden while the project is a still
    Gtk::DropDown videoPresetDrop_;
    Gtk::SpinButton durationSpin_;
    Gtk::SpinButton fpsSpin_;
    bool suspendVideoSync_ = false;  // set while code, not the user, fills them
    // Set while a format fills the spins, so their own handler does not queue
    // a second render on top of the one the format change asks for.
    bool suspendCanvasSync_ = false;
@@ -245,6 +309,10 @@ private:
    Gtk::Label placeholder_;
    Gtk::Spinner spinner_;
    Gtk::Label status_;
    Gtk::Box playbackBar_;  // under the preview of a video only
    Gtk::Button playButton_;
    Gtk::Scale playbackScale_;
    Gtk::Label playbackTime_;
    struct ParamWidget {
        ParamSpec spec;
@@ -13,12 +13,55 @@
 #include "core/image.hpp"
 #include "core/registry.hpp"
 #include "core/rng.hpp"
 #include "core/video.hpp"
 #include "core/version.hpp"
 #include "gui/app.hpp"
 namespace {
 int renderVideo(const effector::Options& options, const std::vector<effector::ChainStage>& stages,
                const std::vector<effector::Image>& sources, std::uint64_t seed) {
    const int count = options.video.frameCount();
    const bool showProgress = isatty(fileno(stderr)) != 0;
    const auto start = std::chrono::steady_clock::now();
    effector::VideoWriter writer(options.output, options.width, options.height, options.video.fps);
    effector::renderFrames(stages, sources, options.width, options.height, seed, {}, options.video,
                           [&](int index, effector::Image&& frame) {
                               writer.write(frame);
                               if (showProgress) {
                                   std::cerr << "\r\033[Kframe " << index + 1 << "/" << count
                                             << std::flush;
                               }
                               return true;
                           });
    if (showProgress) std::cerr << "\r\033[K" << std::flush;
    writer.finish();
    const auto seconds =
        std::chrono::duration<double>(std::chrono::steady_clock::now() - start).count();
    std::cout << options.output << "  " << options.width << "x" << options.height << "  "
              << count << " frames at " << options.video.fps << " fps  effect="
              << effector::chainSlug(stages) << "  seed=" << seed << "  render=" << std::fixed
              << std::setprecision(1) << seconds << " s\n";
    return 0;
 }
 int renderHeadless(const effector::Options& options) {
    // Checked before anything is decoded: a mismatch between what was asked
    // for and the file named is a typo, not something to find out later.
    const bool videoFile = effector::isVideoPath(options.output);
    if (options.video.enabled && !videoFile) {
        std::cerr << "effector: a video is written as .mp4, .mov, .mkv, .webm or .gif, not "
                  << options.output << "\n";
        return 2;
    }
    if (!options.video.enabled && videoFile) {
        std::cerr << "effector: " << options.output
                  << " is a video; give its length with --duration or --video-preset\n";
        return 2;
    }
    auto stages = effector::buildChain(options);
    // A headless run always renders something, so with no -e the default
    // effect stands in. The interface has no such need: it opens on an empty
@@ -54,6 +97,7 @@ int renderHeadless(const effector::Options& options) {
    }
    const std::uint64_t seed = options.seed.value_or(effector::Rng::randomSeed());
    if (options.video.enabled) return renderVideo(options, stages, sources, seed);
    effector::Rng rng(seed);
    const auto start = std::chrono::steady_clock::now();
@@ -25,7 +25,9 @@
 #include "core/rng.hpp"
 #include "core/style.hpp"
 #include "core/version.hpp"
 #include "core/video.hpp"
 #include "effects/blur.hpp"
 #include "effects/channelsplit.hpp"
 #include "effects/grain.hpp"
 #include "effects/monochrome.hpp"
 #include "effects/overlay.hpp"
@@ -1716,6 +1718,239 @@ int main() {
        std::filesystem::remove_all(dir);
    }
    std::cout << "video\n";
    {
        using effector::ChainStage;
        using effector::FrameTime;
        using effector::VideoSettings;
        // Every preset names a canvas format this build offers, and its
        // numbers are ones the project reader and the CLI accept.
        int sound = 0;
        for (const auto& preset : effector::videoPresets()) {
            if (effector::canvasFormatByKey(preset.canvasFormat) != nullptr &&
                preset.seconds >= effector::kMinDuration && preset.seconds <= effector::kMaxDuration &&
                preset.fps >= effector::kMinFps && preset.fps <= effector::kMaxFps &&
                effector::videoPresetByKey(preset.key) == &preset) {
                ++sound;
            }
        }
        check(sound == static_cast<int>(effector::videoPresets().size()),
              "every video preset names a known canvas and a valid length and rate");
        const auto* story = effector::videoPresetByKey("instagram-story");
        check(story != nullptr && story->canvasFormat == "instagram-story" && story->seconds == 15.0,
              "the Instagram story preset is a 15 s vertical clip");
        VideoSettings clip;
        clip.duration = 15.0;
        clip.fps = 30;
        check(clip.frameCount() == 450, "15 s at 30 fps is 450 frames");
        clip.duration = 0.01;
        check(clip.frameCount() == 3, "a clip below the shortest length is clamped to it");
        check(effector::formatSeconds(7.5) == "7.5 s" && effector::formatSeconds(15) == "15 s",
              "lengths read as 7.5 s and 15 s");
        check(effector::isVideoPath("a/b.MP4") && effector::isVideoPath("x.webm") &&
                  effector::isVideoPath("x.gif") && !effector::isVideoPath("x.png") &&
                  !effector::isVideoPath("mp4"),
              "a video is recognised by its extension");
        const auto split = effector::effectByName("channelsplit");
        const std::vector<effector::Image> sources = {gradient(96, 64, 40)};
        // A still ignores every motion param: the picture is the one it
        // always was, whatever they are set to.
        auto calm = split->defaults();
        calm["split_mode"] = std::string("per_band");
        auto wild = calm;
        wild["split_wobble"] = 40L;
        wild["split_jitter"] = 30L;
        wild["split_roll"] = 60L;
        effector::Rng stillA(5);
        effector::Rng stillB(5);
        check(sameBytes(split->render(sources, 96, 64, stillA, calm),
                        split->renderFrame(sources, 96, 64, stillB, wild, FrameTime{})),
              "motion params leave a still untouched");
        check(split->animated(split->defaults()), "channel split moves by default in a video");
        auto frozen = split->defaults();
        frozen["split_wobble"] = 0L;
        frozen["split_jitter"] = 0L;
        frozen["split_roll"] = 0L;
        check(!split->animated(frozen), "and holds still with every motion at 0");
        // A moving stage leaves the shared rng in the same state on every
        // frame, so what comes after it holds still.
        effector::Rng frameA(9);
        effector::Rng frameB(9);
        split->renderFrame(sources, 96, 64, frameA, wild, FrameTime{3, 30, 30});
        split->renderFrame(sources, 96, 64, frameB, wild, FrameTime{17, 30, 30});
        check(frameA.next() == frameB.next(), "every frame leaves the shared rng in one state");
        auto stage = [](const std::string& name, effector::ParamValues values = {}) {
            ChainStage built;
            built.effect = effector::effectByName(name);
            built.values = values.empty() ? built.effect->defaults() : std::move(values);
            return built;
        };
        std::vector<ChainStage> chain = {stage("tiles"), stage("channelsplit", wild), stage("grain")};
        VideoSettings video;
        video.enabled = true;
        video.duration = 1.0;
        video.fps = 8;
        std::vector<effector::Image> first;
        const int handed = effector::renderFrames(chain, sources, 80, 48, 21, {}, video,
                                                  [&](int, effector::Image&& frame) {
                                                      first.push_back(std::move(frame));
                                                      return true;
                                                  });
        check(handed == 8 && first.size() == 8, "a clip hands out every one of its frames");
        std::vector<effector::Image> second;
        effector::renderFrames(chain, sources, 80, 48, 21, {}, video,
                               [&](int, effector::Image&& frame) {
                                   second.push_back(std::move(frame));
                                   return true;
                               });
        bool repeatable = second.size() == first.size();
        for (std::size_t i = 0; repeatable && i < first.size(); ++i) {
            repeatable = sameBytes(first[i], second[i]);
        }
        check(repeatable, "a clip renders byte for byte again from its seed");
        // The still stages before the moving one are rendered once and
        // reused; that shortcut must give exactly what a frame on its own is.
        bool exact = true;
        for (const int index : {0, 3, 7}) {
            effector::Rng rng(21);
            const auto alone = effector::renderChain(chain, sources, 80, 48, rng, {},
                                                     FrameTime{index, 8, 8});
            exact = exact && sameBytes(alone, first[static_cast<std::size_t>(index)]);
        }
        check(exact, "a clip's frame is exactly that frame rendered on its own");
        check(!sameBytes(first[0], first[3]) && !sameBytes(first[3], first[7]),
              "frames of a moving chain differ");
        std::vector<ChainStage> steady = {stage("tiles"), stage("channelsplit", frozen), stage("grain")};
        std::vector<effector::Image> held;
        effector::renderFrames(steady, sources, 80, 48, 21, {}, video,
                               [&](int, effector::Image&& frame) {
                                   held.push_back(std::move(frame));
                                   return true;
                               });
        bool same = held.size() == 8;
        for (const auto& frame : held) same = same && sameBytes(frame, held[0]);
        effector::Rng stillRng(21);
        check(same && sameBytes(held[0], effector::renderChain(steady, sources, 80, 48, stillRng)),
              "a chain that does not move renders its still on every frame");
        int seen = 0;
        effector::renderFrames(chain, sources, 80, 48, 21, {}, video,
                               [&](int, effector::Image&&) { return ++seen < 3; });
        check(seen == 3, "returning false stops a clip early");
        chain[1].enabled = false;
        std::vector<effector::Image> skipped;
        effector::renderFrames(chain, sources, 80, 48, 21, {}, video,
                               [&](int, effector::Image&& frame) {
                                   skipped.push_back(std::move(frame));
                                   return true;
                               });
        check(skipped.size() == 8 && sameBytes(skipped[0], skipped[7]),
              "with the moving stage switched off the clip holds still");
        const auto big = gradient(300, 120, 10);
        const auto small = big.scaledToFit(100);
        check(small.width() == 100 && small.height() == 40, "a preview frame keeps its shape");
        check(big.scaledToFit(400).width() == 300, "a frame already small enough is left alone");
        // The project file: a video says so, a still says nothing about time.
        effector::Project project;
        project.stages = {stage("channelsplit", wild)};
        const auto stillJson = effector::projectToJson(project);
        check(stillJson.find("\"video\"") == std::string::npos, "a still project writes no video");
        check(!effector::projectFromJson(stillJson).video.enabled, "and reads back as a still");
        project.video.enabled = true;
        project.video.duration = 7.5;
        project.video.fps = 24;
        project.video.preset = "instagram-story";
        const auto back = effector::projectFromJson(effector::projectToJson(project));
        check(back.video.enabled && back.video.duration == 7.5 && back.video.fps == 24 &&
                  back.video.preset == "instagram-story",
              "a video project keeps its length, rate and preset");
        const auto motion = back.stages.at(0).values;
        check(effector::paramInt(motion, "split_jitter", 0) == 30 &&
                  effector::paramInt(motion, "split_roll", 0) == 60,
              "and its stages keep their motion");
        const std::string base = "{\"chain\": [{\"effect\": \"blur\"}], \"video\": {\"duration\": ";
        check(!effector::projectFromJson(base + "2, \"preset\": \"cinema\"}}").video.preset.size(),
              "an unknown preset reads as custom");
        bool rejected = false;
        try {
            effector::projectFromJson(base + "2, \"fps\": 500}}");
        } catch (const effector::EffectError&) {
            rejected = true;
        }
        check(rejected, "a frame rate out of range is refused");
        // The command line.
        const auto preset = parsedOptions({"--video-preset", "instagram-story", "-o", "x.mp4"});
        check(preset && preset->video.enabled && preset->width == 1080 && preset->height == 1920 &&
                  preset->video.duration == 15.0 && preset->video.fps == 30 &&
                  preset->video.preset == "instagram-story",
              "--video-preset sets the canvas, length and rate");
        const auto shorter = parsedOptions({"--duration", "5", "--video-preset", "instagram-story"});
        check(shorter && shorter->video.duration == 5.0 && shorter->height == 1920 &&
                  shorter->video.preset.empty(),
              "a length given alongside wins and leaves the preset custom");
        const auto sized = parsedOptions({"--video-preset", "hd-clip", "-s", "320x240"});
        check(sized && sized->width == 320 && sized->format.empty(),
              "a size given alongside wins over the preset's canvas");
        check(!parsedOptions({"--fps", "0"}) && !parsedOptions({"--duration", "abc"}) &&
                  !parsedOptions({"--duration", "400"}) && !parsedOptions({"--video-preset", "vhs"}),
              "a bad rate, length or preset is refused");
        check(!parsedOptions({"-o", "x.png"})->video.enabled, "without them the output is a still");
        bool wrongName = false;
        try {
            effector::VideoWriter writer("clip.png", 16, 16, 30);
        } catch (const effector::EffectError&) {
            wrongName = true;
        }
        check(wrongName, "a video is not written under an image's name");
        if (effector::ffmpegAvailable()) {
            const auto dir = std::filesystem::temp_directory_path() / "effector-video-test";
            std::filesystem::create_directories(dir);
            const auto file = (dir / "clip.mp4").string();
            {
                // Odd sides: the writer pads them for the encoder.
                effector::VideoWriter writer(file, 17, 9, 12);
                for (int i = 0; i < 3; ++i) writer.write(gradient(17, 9, 40 * i));
                writer.finish();
            }
            check(std::filesystem::exists(file) && std::filesystem::file_size(file) > 0,
                  "ffmpeg writes an .mp4 of odd size");
            const auto dropped = (dir / "dropped.webm").string();
            {
                effector::VideoWriter writer(dropped, 16, 16, 12);
                writer.write(gradient(16, 16, 10));
                writer.cancel();
            }
            check(!std::filesystem::exists(dropped), "a cancelled video leaves no file behind");
            bool wrongSize = false;
            try {
                effector::VideoWriter writer((dir / "sized.mp4").string(), 16, 16, 12);
                writer.write(gradient(8, 8, 10));
            } catch (const effector::EffectError&) {
                wrongSize = true;
            }
            check(wrongSize && !std::filesystem::exists(dir / "sized.mp4"),
                  "a frame of the wrong size is refused and the file dropped");
            std::filesystem::remove_all(dir);
        } else {
            std::cout << "  skip writing a video (ffmpeg is not installed)\n";
        }
    }
    std::cout << "version\n";
    {
        // A release is the version in CMakeLists.txt and its entry at the top
@@ -440,6 +440,80 @@ void testRecentProjects(Gtk::Window& window, const std::filesystem::path& dir) {
          "opened projects are listed newest first, a shared name with its folder");
 }
 // Visible labels in the params grid saying `text`.
 bool showsLabel(Gtk::Widget& root, const std::string& text) {
    for (auto* label : all<Gtk::Label>(root)) {
        if (label->get_text() == text && label->is_drawable()) return true;
    }
    return false;
 }
 void testVideo(Gtk::Window& window, const std::filesystem::path& dir) {
    std::cout << "video\n";
    std::filesystem::create_directories(dir);
    const auto path = dir / "moving.json";
    effector::Project project;
    project.stages.push_back({effector::effectByName("channelsplit"), {}});  // needs no sources
    effector::saveProject(path.string(), project);
    window.activate_action("win.open-recent",
                           Glib::Variant<Glib::ustring>::create(Glib::filename_to_uri(path.string())));
    pump(300);
    auto* stack = all<Gtk::Stack>(window).front();
    auto* toggle = named<Gtk::Switch>(window, "video");
    auto* preset = named<Gtk::DropDown>(window, "video-preset");
    auto* duration = named<Gtk::SpinButton>(window, "video-duration");
    auto* width = named<Gtk::SpinButton>(window, "canvas-width");
    auto* height = named<Gtk::SpinButton>(window, "canvas-height");
    auto* playback = named<Gtk::Box>(window, "playback");
    check(toggle != nullptr && preset != nullptr && duration != nullptr && width != nullptr &&
              height != nullptr && playback != nullptr,
          "the video switch, its settings and the playback bar are there");
    if (toggle == nullptr || preset == nullptr || duration == nullptr || width == nullptr ||
        height == nullptr || playback == nullptr) {
        return;
    }
    check(isAncestor(*stack->get_child_by_name("setup"), *toggle), "the video switch is on Setup");
    check(!toggle->get_active() && !preset->is_drawable() && !playback->get_visible(),
          "a still project shows no video settings and no playback");
    check(!showsLabel(window, "Wobble"), "and no motion params for the channel split");
    toggle->set_active(true);
    pump(200);
    check(showsLabel(window, "Wobble") && showsLabel(window, "Tracking bar"),
          "a video shows the channel split's motion params");
    stack->set_visible_child("setup");
    pump(100);
    check(preset->is_drawable() && duration->is_drawable(), "and its preset and length");
    preset->set_selected(1);  // Instagram story, the first preset
    pump(200);
    check(width->get_value() == 1080 && height->get_value() == 1920 && duration->get_value() == 15,
          "Instagram story picks a 1080 × 1920 canvas and 15 s");
    duration->set_value(0.5);
    pump(100);
    check(preset->get_selected() == 0, "changing the length drops the preset to Custom");
    for (int waited = 0; waited < 200 && !playback->get_visible(); ++waited) pump(50);
    check(playback->get_visible(), "the clip is rendered and plays in the preview");
    auto* scale = all<Gtk::Scale>(*playback).empty() ? nullptr : all<Gtk::Scale>(*playback).front();
    const double before = scale != nullptr ? scale->get_value() : -1.0;
    pump(250);
    check(scale != nullptr && scale->get_value() != before, "and it moves on by itself");
    window.activate_action("win.save-project");
    pump(100);
    const auto saved = effector::loadProject(path.string());
    check(saved.video.enabled && saved.video.duration == 0.5 && saved.width == 1080,
          "the project is saved as a video");
    toggle->set_active(false);
    pump(300);
    check(!playback->get_visible() && !showsLabel(window, "Wobble"),
          "switched back to a still, the playback and motion params go");
    stack->set_visible_child("chain");
 }
 }  // namespace
 int main(int argc, char** argv) {
@@ -467,6 +541,7 @@ int main(int argc, char** argv) {
        runTests(*window);
        testHelpWindows(*window);
        testRecentProjects(*window, dataDir / "projects");
        testVideo(*window, dataDir / "video");
        app->remove_window(*window);
    });
    const int status = app->run(argc > 0 ? 1 : 0, argv);