Split effects into image and video effects, with VHS tracking as the first video effect

Effect::video() says which kind an effect is. The Add effect menu lists the two kinds in sections of their own, each scrolling on its own, and offers video effects only in a video project; a video stage carries a film icon in the chain and, in a still, is dimmed and skipped like a stage switched off. enabledStages takes whether the render is a video and is the one place that leaves video stages out of a still. --help groups the video effects under a heading of their own, --list-effects marks them, and a video effect given for a still is skipped with a warning. VideoEffect is the base every video effect builds on, and keeps the rules a moving stage has to follow: it takes one value from the shared rng, the same on every frame, and hands the effect steady and per-frame generators and loop-rounded time through a Moment, so a subclass writes only animate(). VHS tracking is the first, and the one to copy: the colour planes sway and shake and a tracking bar rolls down the picture. That motion moves out of channel split, which is an image effect again and renders stills exactly as before; forVideo() goes with it. Version 0.7.0. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
2026-09-26 19:03:39 +02:00
parent ea59db5acd
commit cdaadffc89
23 changed files with 752 additions and 376 deletions
@@ -4,6 +4,26 @@ 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.
 ## [0.7.0] - 2026-09-26
 ### Added
 - Effects are image effects or video effects. The Add effect menu lists them
  in two sections, each under its own heading, and offers video effects only
  in a video project. In the chain a video stage has a film icon, and in a
  still it is dimmed and skipped, like a stage that is switched off.
 - VHS tracking, the first video effect: the colour planes sway and shake, and
  a tracking bar rolls down the picture. On the command line it is
  `-e tracking` with `--tracking-wobble`, `--tracking-jitter`, `--tracking-bar`
  and the rest.
 - `--help` lists the video effects under a heading of their own, and
  `--list-effects` marks them. A video effect given for a still is skipped
  with a warning.
 ### Changed
 - Channel split is an image effect again. Its motion (Wobble, Jitter, Tracking
  bar) has moved to VHS tracking, so a 0.6 video project that moved its channel
  split needs a VHS tracking stage after it. Stills are unchanged.
 ## [0.6.1] - 2026-09-26
 ### Fixed
@@ -95,7 +95,8 @@ first stage ever sees the sources, so `chainNeedsSources` (`src/core/chain.cpp`)
 just asks the first stage — a chain led by blur renders with no images loaded at
 all, and both front-ends gate on that rather than on "are there any images".
-Adding an effect: new `src/effects/<name>.{hpp,cpp}` subclassing `Effect`, one
+Adding an effect: new `src/effects/<name>.{hpp,cpp}` subclassing `Effect` (or
 `VideoEffect` for one that moves, see "Video projects"), one
 line in the registry list in `src/core/registry.cpp`, one line in the
 `effector_core` sources in `CMakeLists.txt`. Nothing else — it shows up in the
 CLI, in the chain menu and as a cascade stage on its own.
@@ -181,22 +182,39 @@ 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,
+Effects are of two kinds, and `Effect::video()` says which. An *image effect*
-`fps == 0`, is a still) through `Effect::renderFrame`, which falls back to
+(the default) makes a picture and holds still in a clip; it overrides only
-`render` — an effect that does not move overrides nothing. One that moves
+`render`, which `Effect::renderFrame` falls back to. A *video effect* is motion
-overrides `renderFrame` and `animated(values)`, and marks its motion params
+and nothing else. `enabledStages(stages, video)` is where the kinds meet the
-`.forVideo()`: the interface hides those in a still project (declaratively,
+chain: in a still, a video stage is left out exactly like a disabled one,
-like `.styled()`), the CLI still has their flags. A still must render byte for
+drawing nothing from the rng. So `renderChain` (by `frame.video()`),
-byte what it did before the effect learned to move.
+`chainNeedsSources`, `chainTitle` and `chainSlug` all take whether the render is
 a video. The interface builds the split from `video()` alone: two sections in
 the Add effect menu, with the video section insensitive in a still, a
 `camera-video-symbolic` icon on a video stage's row, and the row dimmed while a
 still skips it. The CLI groups `--help` the same way and warns when it skips one.
 A video effect subclasses `VideoEffect` (`src/effects/video_effect.hpp`), not
 `Effect`, and writes only `animate(input, values, const Moment& at)`. The base
 keeps the rules. It takes the input crop and exactly one value from the shared
 rng, the same on every frame, and hands out randomness through the `Moment`:
 `at.steady()` gives the same draws every frame (phases, directions),
 `at.fresh()` gives new draws per frame (shake, noise). It hands out time as
 `at.cycle(perSecond)`, rounded through `loopRate` to a whole number of cycles so
 the clip loops without a jump. `TrackingEffect` (`src/effects/tracking.cpp`,
 "VHS tracking") is the reference: copy its layout (params, a `Settings` struct,
 steady draws, time, fresh draws, one parallel pixel pass) for the next one.
 Registering it is the same one line in `registry.cpp`, after the comment that
 starts the video effects. There is no per-param video flag: motion is a video
 effect of its own, never extra params on an image effect.
 `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
+`Rng(seed)`, so an image effect draws the same values every frame and holds
-and holds still. A moving effect must therefore leave the shared rng in the
+still, and because `VideoEffect` leaves the shared rng in one state, the stages
-same state on every frame — the channel split draws its per-frame shake from a
+after a video effect hold still too. The stages before the first video effect
-generator of its own, seeded by one draw — or everything after it would flicker.
+are rendered once and their image and rng state reused. The `video` tests
-The stages before the first `animated()` one are rendered once and their image
+assert that frame k is exactly `renderChain(..., FrameTime{k, ...})`, so that
-and rng state reused; the `video` tests assert that frame k is exactly
+shortcut can never change output.
 `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.
@@ -1,5 +1,5 @@
 cmake_minimum_required(VERSION 3.20)
-project(effector VERSION 0.6.1 LANGUAGES CXX)
+project(effector VERSION 0.7.0 LANGUAGES CXX)
 set(CMAKE_CXX_STANDARD 20)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
@@ -56,6 +56,8 @@ add_library(effector_core STATIC
    src/effects/slitshift.cpp
    src/effects/text.cpp
    src/effects/tiles.cpp
    src/effects/tracking.cpp
    src/effects/video_effect.cpp
    src/effects/warp.cpp
 )
 target_include_directories(effector_core PUBLIC src ${CMAKE_CURRENT_BINARY_DIR}/generated)
@@ -73,18 +73,23 @@ 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 story.mp4 --video-preset instagram-story -e channelsplit -e tracking --seed 1 photo.jpg
-build/effector -o loop.gif -s 480x480 --duration 3 --fps 15 -e channelsplit photo.jpg
+build/effector -o loop.gif -s 480x480 --duration 3 --fps 15 -e tracking --tracking-bar 40 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
+whatever was not given alongside it.
-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
+Effects come in two kinds. **Image effects** make a picture and hold still in a
-picture, like a worn tape on an old tube. Its motion params only show in a
+clip. **Video effects** are motion: the Add effect menu lists them under a
-video project, and a still renders exactly as before. Every frame starts from
+heading of their own, and they can only be added once the project is a video.
-the same seed, so stages that do not move hold still while one that does
+In a still project a video stage is marked as skipped and the render leaves it
-moves, and a clip renders frame for frame the same again.
+out, as it would a stage that is switched off. For now there is one video
 effect, **VHS tracking**: the colour planes sway and shake, and a tracking bar
 rolls down the picture, like a worn tape on an old tube. Put it after the
 image effects it should shake. Every frame starts from the same seed, so the
 image effects hold still while a video effect moves them, 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).
@@ -2,7 +2,7 @@
 # so pkgver must follow the project() line of CMakeLists.txt (the version core
 # test checks it). From this folder: makepkg -si
 pkgname=effector
-pkgver=0.6.1
+pkgver=0.7.0
 pkgrel=1
 pkgdesc='Image effects app: a GTK4 interface and a headless CLI over pluggable effects'
 arch=('x86_64' 'aarch64')
@@ -264,15 +264,22 @@ std::string usage(const char* programName) {
        out << "  " << preset.label << ", " << videoPresetDetail(preset) << "\n";
    }
-    for (const auto& effect : effects()) {
+    // Image effects first, then the video effects under a heading of their
-        out << "\n" << effect->title() << " options:\n";
+    // own: those run only in a clip.
-        for (const auto& spec : effect->params()) {
+    for (const bool video : {false, true}) {
-            std::string flag = spec.flag();
+        if (video) {
-            if (spec.type != ParamSpec::Type::Bool) flag += " VALUE";
+            out << "\nVideo effects, which run only in a video (--duration or --video-preset):\n";
-            out << "  " << flag;
+        }
-            if (flag.size() < 20) out << std::string(20 - flag.size(), ' ');
+        for (const auto& effect : effects()) {
-            out << "  " << (spec.help.empty() ? spec.label : spec.help)
+            if (effect->video() != video) continue;
-                << (spec.videoOnly ? " (video only)" : "") << "\n";
+            out << "\n" << effect->title() << " options (-e " << effect->name() << "):\n";
            for (const auto& spec : effect->params()) {
                std::string flag = spec.flag();
                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";
            }
        }
    }
    return out.str();
@@ -6,11 +6,13 @@
 namespace effector {
-std::vector<const ChainStage*> enabledStages(const std::vector<ChainStage>& stages) {
+std::vector<const ChainStage*> enabledStages(const std::vector<ChainStage>& stages, bool video) {
    std::vector<const ChainStage*> running;
    running.reserve(stages.size());
    for (const auto& stage : stages) {
-        if (stage.enabled && stage.effect) running.push_back(&stage);
+        if (stage.enabled && stage.effect && (video || !stage.effect->video())) {
            running.push_back(&stage);
        }
    }
    return running;
 }
@@ -36,7 +38,7 @@ ParamValues stageValues(const ChainStage& stage, const StyleSet& styles) {
 namespace {
 // The stages that run, checked: throws for a chain with nothing to render.
-std::vector<const ChainStage*> runningStages(const std::vector<ChainStage>& stages) {
+std::vector<const ChainStage*> runningStages(const std::vector<ChainStage>& stages, bool video) {
    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.");
@@ -44,9 +46,17 @@ std::vector<const ChainStage*> runningStages(const std::vector<ChainStage>& stag
    // 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.
+    // back exactly the picture the chain made before it was added. A video
-    auto running = enabledStages(stages);
+    // effect in a still is left out the same way.
-    if (running.empty()) throw EffectError("Every effect in the chain is disabled.");
+    auto running = enabledStages(stages, video);
    if (running.empty()) {
        const bool videoLeft = std::any_of(stages.begin(), stages.end(), [](const ChainStage& stage) {
            return stage.enabled && stage.effect->video();
        });
        throw EffectError(videoLeft ? "Video effects only run in a video, and the chain has "
                                      "no image effect switched on."
                                    : "Every effect in the chain is disabled.");
    }
    return running;
 }
@@ -99,37 +109,27 @@ Image runStages(const std::vector<const ChainStage*>& running, std::size_t first
 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);
+    const auto running = runningStages(stages, frame.video());
    ensureRenderFits(running, width, height, styles);
    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 auto running = runningStages(stages, true);
    ensureRenderFits(running, width, height, styles);
    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
+    // Everything before the first video effect is the same on every frame --
-    // frame -- the same seed, the same values, no time -- so it is rendered
+    // the same seed, the same values, no time -- so it is rendered once, as
-    // once, as frame 0, and picked up from there. The rng is copied along
+    // frame 0, and picked up from there. The rng is copied along with the
-    // with the picture, which is what makes the shortcut exact.
+    // picture, which is what makes the shortcut exact.
    std::size_t still = 0;
-    while (still < running.size() &&
+    while (still < running.size() && !running[still]->effect->video()) ++still;
           !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});
@@ -146,24 +146,24 @@ int renderFrames(const std::vector<ChainStage>& stages, const std::vector<Image>
    return count;
 }
-bool chainNeedsSources(const std::vector<ChainStage>& stages) {
+bool chainNeedsSources(const std::vector<ChainStage>& stages, bool video) {
-    const auto running = enabledStages(stages);
+    const auto running = enabledStages(stages, video);
    if (running.empty()) return false;
    return running.front()->effect->needsSources();
 }
-std::string chainTitle(const std::vector<ChainStage>& stages) {
+std::string chainTitle(const std::vector<ChainStage>& stages, bool video) {
    std::string text;
-    for (const auto* stage : enabledStages(stages)) {
+    for (const auto* stage : enabledStages(stages, video)) {
        if (!text.empty()) text += " → ";
        text += stage->effect->title();
    }
    return text;
 }
-std::string chainSlug(const std::vector<ChainStage>& stages) {
+std::string chainSlug(const std::vector<ChainStage>& stages, bool video) {
    std::string text;
-    for (const auto* stage : enabledStages(stages)) {
+    for (const auto* stage : enabledStages(stages, video)) {
        if (!text.empty()) text += "-";
        text += stage->effect->name();
    }
@@ -40,11 +40,12 @@ struct ChainStage {
 // that style carries. The one place a style is resolved.
 ParamValues stageValues(const ChainStage& stage, const StyleSet& styles);
-// The stages that actually run, in order, as pointers into `stages`. A
+// The stages that actually run, in order, as pointers into `stages`: those
-// disabled stage draws nothing from the rng and is handed no image, so a chain
+// switched on, and of those the video effects only in a video. A stage left
-// renders exactly as it would if that stage had never been added -- this is
+// out draws nothing from the rng and is handed no image, so a chain renders
-// the one place the rest of the code asks what "disabled" means.
+// exactly as it would if that stage had never been added -- this is the one
-std::vector<const ChainStage*> enabledStages(const std::vector<ChainStage>& stages);
+// place the rest of the code asks what "disabled" means.
 std::vector<const ChainStage*> enabledStages(const std::vector<ChainStage>& stages, bool video);
 // Renders the enabled stages in order. The first one sees the loaded sources;
 // every later one sees the previous stage's output as its only source, so blur
@@ -55,21 +56,19 @@ std::vector<const ChainStage*> enabledStages(const std::vector<ChainStage>& stag
 // `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
+// `frame` says where in a video the render sits, a still by default, in
-// stage is handed it, and only one that moves makes anything of it.
+// which the video effects are skipped; every stage that runs is handed it,
 // and only a video effect 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 = {},
                  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
+// frame. The stages before the first video effect 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,
@@ -80,13 +79,13 @@ int renderFrames(const std::vector<ChainStage>& stages, const std::vector<Image>
 // 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
 // is simply whether that effect declares that it needs them.
-bool chainNeedsSources(const std::vector<ChainStage>& stages);
+bool chainNeedsSources(const std::vector<ChainStage>& stages, bool video);
 // "Scanlines → Blur", for window titles and status lines. Both of these name
-// what was rendered, so a disabled stage is left out of them.
+// what was rendered, so a stage that did not run is left out of them.
-std::string chainTitle(const std::vector<ChainStage>& stages);
+std::string chainTitle(const std::vector<ChainStage>& stages, bool video);
 // "scanlines-blur", for file names.
-std::string chainSlug(const std::vector<ChainStage>& stages);
+std::string chainSlug(const std::vector<ChainStage>& stages, bool video);
 }  // namespace effector
@@ -58,21 +58,22 @@ public:
        return title();
    }
-    // Whether a stage with these values changes from one frame of a video to
+    // Whether this is a video effect rather than an image effect. An image
-    // the next. A stage that does not is rendered once for the whole clip.
+    // effect makes a picture and holds still in a clip; a video effect is
-    virtual bool animated(const ParamValues& values) const {
+    // motion and nothing else, so it is offered only in a video project and a
-        (void)values;
+    // still skips it whole, as it skips a stage that is switched off. Video
-        return false;
+    // effects derive from VideoEffect (effects/video_effect.hpp), which
-    }
+    // answers true here and keeps the rules a moving stage has to follow.
    virtual bool video() const { 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
+    // One frame of a video, or a still when `frame` says so. An image effect
-    // does not move needs only render(), which this falls back to. One that
+    // needs only render(), which this falls back to; a video effect renders
-    // does must leave `rng` in the same state on every frame -- a frame's own
+    // here, and must leave `rng` in the same state on every frame -- a
-    // randomness comes from a generator of its own -- so the stages after it
+    // frame's own randomness comes from a generator of its own -- so the
-    // stay put while it moves.
+    // 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;
@@ -16,12 +16,6 @@ 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;
@@ -27,10 +27,6 @@ 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"
@@ -38,9 +34,6 @@ 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);
@@ -14,6 +14,7 @@
 #include "effects/slitshift.hpp"
 #include "effects/text.hpp"
 #include "effects/tiles.hpp"
 #include "effects/tracking.hpp"
 #include "effects/warp.hpp"
 namespace effector {
@@ -36,6 +37,8 @@ const std::vector<EffectPtr>& effects() {
        std::make_shared<WarpEffect>(),
        std::make_shared<BitCrushEffect>(),
        std::make_shared<FeedbackEffect>(),
        // Video effects, offered only in a video project.
        std::make_shared<TrackingEffect>(),
    };
    return registry;
 }
@@ -2,8 +2,6 @@
 #include <algorithm>
 #include <array>
 #include <cmath>
 #include <numbers>
 #include <vector>
 #include "core/parallel.hpp"
@@ -24,26 +22,6 @@ 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;
 }
@@ -57,68 +35,28 @@ struct Offset {
 using ChannelOffsets = std::array<Offset, 3>;
-ChannelOffsets drawOffsets(Rng& rng, int amount, const std::string& channels, int& moved) {
+ChannelOffsets drawOffsets(Rng& rng, int amount, const std::string& channels) {
    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") {
-        moved = static_cast<int>(rng.below(2));
+        offsets[rng.below(2)] = draw();
        offsets[static_cast<std::size_t>(moved)] = draw();
    } else {
        for (auto& offset : offsets) offset = draw();
    }
    return offsets;
 }
-// A motion of each channel, handed out the way the mode moves channels: all
+}  // namespace
 // 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>;
-Motion spread(const Motion& motion, const std::string& channels, int moved) {
+Image ChannelSplitEffect::render(const std::vector<Image>& sources, int width, int height, Rng& rng,
-    if (channels == "red_cyan") return {motion[0], -motion[0], -motion[0]};
+                                 const ParamValues& values) const {
    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)));
@@ -133,105 +71,20 @@ Image renderSplit(const std::vector<Image>& sources, int width, int height, Rng&
    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));
-    moved.reserve(static_cast<std::size_t>(bandCount));
+    for (int i = 0; i < bandCount; ++i) plan.push_back(drawOffsets(rng, amount, channels));
    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 = rows[y];
+            const ChannelOffsets& offsets = plan[y / static_cast<std::size_t>(band)];
            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 - dx, 0, width - 1);
+                    const int sx = std::clamp(x - offset.dx, 0, width - 1);
                    out[static_cast<std::size_t>(x) * 3 + c] = in[static_cast<std::size_t>(sx) * 3 + c];
                }
            }
@@ -241,21 +94,4 @@ Image renderSplit(const std::vector<Image>& sources, int width, int height, Rng&
    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
@@ -6,9 +6,6 @@ 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 {
@@ -21,12 +18,9 @@ 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
@@ -0,0 +1,147 @@
 #include "effects/tracking.hpp"
 #include <algorithm>
 #include <array>
 #include <cmath>
 #include <numbers>
 #include <vector>
 #include "core/parallel.hpp"
 namespace effector {
 const std::vector<ParamSpec>& TrackingEffect::params() const {
    static const std::vector<ParamSpec> specs = {
        ParamSpec::makeInt("tracking_wobble", "Wobble", 4, 0, 256,
                           "How far in pixels the colour planes sway apart and back."),
        ParamSpec::makeDouble("tracking_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),
        ParamSpec::makeInt("tracking_jitter", "Jitter", 2, 0, 256,
                           "Furthest in pixels a band shakes, anew on every frame."),
        ParamSpec::makeInt("tracking_band_height", "Band height", 24, 1, 2048,
                           "Thickness in pixels of the bands that shake on their own."),
        ParamSpec::makeInt("tracking_bar", "Tracking bar", 16, 0, 512,
                           "How far in pixels the rolling bar tears the rows sideways and the "
                           "colour planes apart; 0 for none."),
        ParamSpec::makeDouble("tracking_bar_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),
    };
    return specs;
 }
 namespace {
 struct Settings {
    int wobble;
    double wobbleSpeed;
    int jitter;
    int band;
    int bar;
    double barTime;
    explicit Settings(const ParamValues& values)
        : wobble(static_cast<int>(std::max(0L, paramInt(values, "tracking_wobble", 4)))),
          wobbleSpeed(std::max(0.0, paramDouble(values, "tracking_wobble_speed", 0.5))),
          jitter(static_cast<int>(std::max(0L, paramInt(values, "tracking_jitter", 2)))),
          band(static_cast<int>(std::max(1L, paramInt(values, "tracking_band_height", 24)))),
          bar(static_cast<int>(std::max(0L, paramInt(values, "tracking_bar", 16)))),
          barTime(std::max(0.5, paramDouble(values, "tracking_bar_time", 4.0))) {}
 };
 double unit(Rng& rng) { return static_cast<double>(rng.next() >> 11) * 0x1.0p-53; }
 // How far each of the red, green and blue planes is moved on one row.
 struct RowShift {
    std::array<int, 3> dx{};
    std::array<int, 3> dy{};
 };
 }  // namespace
 Image TrackingEffect::animate(Image input, const ParamValues& values, const Moment& at) const {
    const Settings settings(values);
    const int width = input.width();
    const int height = input.height();
    constexpr double tau = 2.0 * std::numbers::pi;
    // What stays put for the whole clip: where each plane's sway starts, and
    // the direction it sways in.
    Rng steady = at.steady();
    std::array<double, 3> phase{};
    std::array<double, 3> angle{};
    for (std::size_t c = 0; c < 3; ++c) {
        phase[c] = unit(steady) * tau;
        angle[c] = unit(steady) * tau;
    }
    // Where this frame is in time: the sway of each plane, and the bar -- an
    // eighth of the picture, soft at both edges, entering above the top and
    // leaving below the bottom.
    std::array<double, 3> swayX{};
    std::array<double, 3> swayY{};
    if (settings.wobble > 0 && settings.wobbleSpeed > 0.0) {
        const double turn = at.cycle(settings.wobbleSpeed) * tau;
        for (std::size_t c = 0; c < 3; ++c) {
            const double sway = settings.wobble * std::sin(turn + phase[c]);
            swayX[c] = sway * std::cos(angle[c]);
            swayY[c] = sway * std::sin(angle[c]);
        }
    }
    const double barHeight = std::max(8.0, height / 8.0);
    const double barTop = -barHeight + at.cycle(1.0 / settings.barTime) * (height + barHeight);
    // What changes on every frame: each band's shake, mostly sideways, as a
    // picture losing its horizontal hold. All of it drawn, band by band,
    // before a pixel is touched.
    Rng fresh = at.fresh();
    std::vector<RowShift> rows(static_cast<std::size_t>(height));
    std::vector<int> tear(static_cast<std::size_t>(height), 0);
    for (int top = 0; top < height; top += settings.band) {
        std::array<double, 3> jitterX{};
        std::array<double, 3> jitterY{};
        if (settings.jitter > 0) {
            for (std::size_t c = 0; c < 3; ++c) {
                jitterX[c] = static_cast<double>(fresh.inRange(-settings.jitter, settings.jitter));
                jitterY[c] = static_cast<double>(fresh.inRange(-settings.jitter, settings.jitter)) / 3.0;
            }
        }
        const int end = std::min(height, top + settings.band);
        for (int y = top; y < end; ++y) {
            // The bar pulls red one way and blue the other, and drags the
            // whole row half as far.
            double pull = 0.0;
            if (settings.bar > 0 && y >= barTop && y < barTop + barHeight) {
                pull = settings.bar * std::sin(std::numbers::pi * (y - barTop) / barHeight);
            }
            constexpr std::array<double, 3> apart = {1.0, 0.0, -1.0};
            auto& row = rows[static_cast<std::size_t>(y)];
            for (std::size_t c = 0; c < 3; ++c) {
                row.dx[c] = static_cast<int>(std::lround(swayX[c] + jitterX[c] + pull * apart[c]));
                row.dy[c] = static_cast<int>(std::lround(swayY[c] + jitterY[c]));
            }
            tear[static_cast<std::size_t>(y)] = static_cast<int>(std::lround(pull / 2.0));
        }
    }
    Image frame(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) {
            std::uint8_t* out = frame.row(static_cast<int>(y));
            for (std::size_t c = 0; c < 3; ++c) {
                const int dx = rows[y].dx[c] + tear[y];
                const int sy = std::clamp(static_cast<int>(y) - rows[y].dy[c], 0, height - 1);
                const std::uint8_t* in = input.row(sy);
                for (int x = 0; x < width; ++x) {
                    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];
                }
            }
        }
    });
    return frame;
 }
 }  // namespace effector
@@ -0,0 +1,29 @@
 #pragma once
 #include "effects/video_effect.hpp"
 namespace effector {
 // A worn tape losing its hold: the red, green and blue planes sway apart and
 // back, bands of the picture shake sideways from frame to frame, and a
 // tracking bar rolls down the picture tearing the rows it passes.
 //
 // The first video effect, and the one to copy for the next: its params are
 // declared like any effect's, and animate() reads them, takes what stays put
 // from at.steady(), what changes every frame from at.fresh(), and time from
 // at.cycle() -- then draws the frame in one pass over the pixels.
 class TrackingEffect : public VideoEffect {
 public:
    std::string name() const override { return "tracking"; }
    std::string title() const override { return "VHS tracking"; }
    std::string description() const override {
        return "A worn tape losing its hold: the colour planes sway and shake, and a tracking bar "
               "rolls down the picture.";
    }
    const std::vector<ParamSpec>& params() const override;
 protected:
    Image animate(Image input, const ParamValues& values, const Moment& at) const override;
 };
 }  // namespace effector
@@ -0,0 +1,47 @@
 #include "effects/video_effect.hpp"
 #include <algorithm>
 #include <cmath>
 #include "core/video.hpp"
 #include "effects/source_fill.hpp"
 namespace effector {
 double Moment::length() const noexcept {
    return static_cast<double>(std::max(1, frame_.count)) / std::max(1, frame_.fps);
 }
 double Moment::loopRate(double perSecond) const noexcept {
    const double clip = length();
    return std::max(1.0, std::round(perSecond * clip)) / clip;
 }
 double Moment::cycle(double perSecond) const noexcept {
    return std::fmod(seconds() * loopRate(perSecond), 1.0);
 }
 Rng Moment::fresh() const noexcept {
    return Rng(seed_ ^ (0x9e3779b97f4a7c15ULL * static_cast<std::uint64_t>(frame_.index + 1)));
 }
 Image VideoEffect::render(const std::vector<Image>& sources, int width, int height, Rng& rng,
                          const ParamValues& values) const {
    return renderFrame(sources, width, height, rng, values, FrameTime{0, kDefaultFps, kDefaultFps});
 }
 Image VideoEffect::renderFrame(const std::vector<Image>& sources, int width, int height, Rng& rng,
                               const ParamValues& values, const FrameTime& frame) const {
    if (width < 1 || height < 1) throw EffectError("Canvas size must be at least 1x1 pixels.");
    const FrameTime at = frame.video() ? frame : FrameTime{0, kDefaultFps, kDefaultFps};
    // Both of these take the same values from the shared rng on every frame:
    // the crop a leading stage starts from, and the one seed everything the
    // effect draws comes from.
    Image input = canvasFromSources(sources, width, height, rng);
    const std::uint64_t seed = rng.next();
    return animate(std::move(input), values, Moment(at, seed));
 }
 }  // namespace effector
@@ -0,0 +1,79 @@
 #pragma once
 #include <cstdint>
 #include <vector>
 #include "core/effect.hpp"
 namespace effector {
 // Where one frame sits in its clip, and the randomness it may draw on, as a
 // video effect is handed it. Time is always read through here: the rates it
 // hands out are rounded to fit the clip, so whatever an effect does with
 // them, the last frame leads straight back into the first and a clip loops
 // without a jump.
 class Moment {
 public:
    Moment(const FrameTime& frame, std::uint64_t seed) noexcept : frame_(frame), seed_(seed) {}
    int index() const noexcept { return frame_.index; }
    int frames() const noexcept { return frame_.count; }
    int fps() const noexcept { return frame_.fps; }
    double seconds() const noexcept { return frame_.seconds(); }  // into the clip
    double length() const noexcept;                              // of the whole clip
    // The rate nearest `perSecond` at which a whole number of cycles fits the
    // clip, and never fewer than one.
    double loopRate(double perSecond) const noexcept;
    // How far through a cycle that happens `perSecond` times a second this
    // frame is, from 0 at its start towards 1 at its end: the one number most
    // motion needs -- sin(2π · cycle) sways, cycle · height rolls down.
    double cycle(double perSecond) const noexcept;
    // Draws that come out the same on every frame of the clip: where a sway
    // starts, which way it goes -- what makes the motion this seed's own.
    Rng steady() const noexcept { return Rng(seed_); }
    // Draws that are new on every frame: shake, noise, flicker. The same
    // frame of the same seed still draws the same values, so frames can be
    // rendered alone and in any order.
    Rng fresh() const noexcept;
 private:
    FrameTime frame_;
    std::uint64_t seed_;
 };
 // The base of every video effect, and the one place that keeps the rules a
 // moving stage has to follow, so an effect built on it is only its look:
 //
 // - It takes one value from the shared rng -- the same on every frame -- and
 //   hands the effect generators of its own through the Moment. The stages
 //   after it therefore see the rng in one state throughout and hold still
 //   while it moves.
 // - It is a transform: it needs no source images, and leading a chain it
 //   starts from a crop of one, as the other transforms do.
 // - It never runs in a still project (the chain skips it). Asked for a still
 //   directly, it gives the first frame of a one-second clip.
 //
 // A new video effect subclasses this, declares its params like any effect,
 // and writes animate(); see TrackingEffect for one.
 class VideoEffect : public Effect {
 public:
    bool video() const final { return true; }
    bool needsSources() const final { return false; }
    Image render(const std::vector<Image>& sources, int width, int height, Rng& rng,
                 const ParamValues& values) const final;
    Image renderFrame(const std::vector<Image>& sources, int width, int height, Rng& rng,
                      const ParamValues& values, const FrameTime& frame) const final;
 protected:
    // One frame of the clip: `input` is the picture this stage is handed,
    // already at the canvas size, and what comes back is the same size.
    // Every random value comes from `at`, never from anywhere else.
    virtual Image animate(Image input, const ParamValues& values, const Moment& at) const = 0;
 };
 }  // namespace effector
@@ -381,7 +381,7 @@ Gtk::Widget& EffectorWindow::buildSetupTab() {
 // rather than left there to be filled in vain. This is the same declarative
 // answer the render gate uses -- no effect is named here.
 void EffectorWindow::updateSourcesVisible() {
-    sourcesSection_.set_visible(chainNeedsSources(stages_));
+    sourcesSection_.set_visible(chainNeedsSources(stages_, isVideo()));
 }
 // The heading carries the count, which a long list scrolled away would hide.
@@ -608,7 +608,9 @@ void EffectorWindow::setVideoSettings(const VideoSettings& video) {
    suspendVideoSync_ = suspended;
    playbackBar_.set_visible(false);
    clearClip();
-    buildParamWidgets();  // the motion params come and go with the switch
+    updateVideoEffectItems();
    rebuildChainRows();  // a video stage runs or is skipped with the switch
    buildParamWidgets();
 }
 void EffectorWindow::onVideoToggled() {
@@ -619,6 +621,8 @@ void EffectorWindow::onVideoToggled() {
    result_ = Image();
    clearClip();
    saveButton_.set_sensitive(false);
    updateVideoEffectItems();
    rebuildChainRows();  // a video stage runs or is skipped with the switch
    buildParamWidgets();
    requestRender();
 }
@@ -805,8 +809,11 @@ void EffectorWindow::buildParamWidgets() {
    const auto& stage = stages_[static_cast<std::size_t>(selectedStage_)];
    // The settings of a stage that is switched off stay editable: it is still
    // being worked on, it just is not in the picture for the moment.
    const bool skipped = stage.effect->video() && !isVideo();
    paramHeading_.set_text(std::to_string(selectedStage_ + 1) + ". " + stage.effect->title() +
-                           (stage.enabled ? " settings" : " settings (off)"));
+                           (!stage.enabled ? " settings (off)"
                            : skipped      ? " settings (video only)"
                                           : " settings"));
    int row = 0;
    // The style the stage follows, when its effect takes one at all: the
@@ -829,9 +836,6 @@ 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;
@@ -1707,39 +1711,86 @@ Gtk::Widget& EffectorWindow::buildChainSection() {
    return *box;
 }
-// The tallest the menu of effects grows before it scrolls, in pixels.
+// The tallest each part of the menu of effects grows before it scrolls, in
-constexpr int addMenuMaxHeight = 480;
+// pixels: together, with their headings, short enough to open below a button
 // near the top of a small screen.
 constexpr int addMenuImageHeight = 330;
 constexpr int addMenuVideoHeight = 110;
 // One entry per registered effect, so a new effect shows up here without this
-// file knowing anything about it.
+// file knowing anything about it. The image effects and the video effects
 // are two sections, each under its own heading and each scrolling on its own,
 // so the video effects stay in sight however many image effects there are;
 // they can only be picked in a video project.
 Gtk::Widget& EffectorWindow::buildAddMenu() {
    auto* popover = Gtk::make_managed<Gtk::Popover>();
-    auto* list = Gtk::make_managed<Gtk::Box>(Gtk::Orientation::VERTICAL, 2);
+    auto* sections = Gtk::make_managed<Gtk::Box>(Gtk::Orientation::VERTICAL, 2);
-    for (const auto& effect : effects_) {
+    for (const bool video : {false, true}) {
-        auto* item = Gtk::make_managed<Gtk::Button>(effect->title());
+        if (video) {
-        item->add_css_class("flat");
+            auto* separator = Gtk::make_managed<Gtk::Separator>();
-        item->set_tooltip_text(effect->description());
+            separator->set_margin_top(6);
-        if (auto* child = dynamic_cast<Gtk::Label*>(item->get_child())) child->set_xalign(0.0F);
+            separator->set_margin_bottom(4);
-        item->signal_clicked().connect([this, effect] {
+            sections->append(*separator);
-            addEffectButton_.popdown();
+        }
-            appendStage(effect);
+        auto* heading = Gtk::make_managed<Gtk::Box>(Gtk::Orientation::HORIZONTAL, 6);
-        });
+        heading->set_margin_start(8);
-        list->append(*item);
+        heading->set_margin_top(4);
        heading->set_margin_bottom(2);
        heading->append(*Gtk::make_managed<Gtk::Image>(Gio::ThemedIcon::create(
            video ? "camera-video-symbolic" : "camera-photo-symbolic")));
        auto* title = Gtk::make_managed<Gtk::Label>(video ? "Video effects" : "Image effects");
        title->add_css_class("heading");
        heading->append(*title);
        sections->append(*heading);
        if (video) {
            videoEffectsHint_ = Gtk::make_managed<Gtk::Label>("Switch on Video under Setup to add these.");
            videoEffectsHint_->add_css_class("dim-label");
            videoEffectsHint_->set_xalign(0.0F);
            videoEffectsHint_->set_margin_start(8);
            videoEffectsHint_->set_wrap(true);
            videoEffectsHint_->set_max_width_chars(28);
            sections->append(*videoEffectsHint_);
        }
        auto* list = Gtk::make_managed<Gtk::Box>(Gtk::Orientation::VERTICAL, 2);
        for (const auto& effect : effects_) {
            if (effect->video() != video) continue;
            auto* item = Gtk::make_managed<Gtk::Button>(effect->title());
            item->add_css_class("flat");
            item->set_tooltip_text(effect->description());
            if (auto* child = dynamic_cast<Gtk::Label*>(item->get_child())) child->set_xalign(0.0F);
            item->signal_clicked().connect([this, effect] {
                addEffectButton_.popdown();
                appendStage(effect);
            });
            if (video) videoEffectItems_.push_back(item);
            list->append(*item);
        }
        // A popover that does not fit on the screen is not shown at all, and
        // the lists grow with every effect registered, so past a point they
        // scroll.
        auto* scroller = Gtk::make_managed<Gtk::ScrolledWindow>();
        scroller->set_policy(Gtk::PolicyType::NEVER, Gtk::PolicyType::AUTOMATIC);
        scroller->set_propagate_natural_height(true);
        scroller->set_max_content_height(video ? addMenuVideoHeight : addMenuImageHeight);
        scroller->set_child(*list);
        sections->append(*scroller);
    }
    updateVideoEffectItems();
-    // A popover that does not fit on the screen is not shown at all, and the
+    popover->set_child(*sections);
    // list grows with every effect registered, so past a point it scrolls.
    auto* scroller = Gtk::make_managed<Gtk::ScrolledWindow>();
    scroller->set_policy(Gtk::PolicyType::NEVER, Gtk::PolicyType::AUTOMATIC);
    scroller->set_propagate_natural_height(true);
    scroller->set_max_content_height(addMenuMaxHeight);
    scroller->set_child(*list);
    popover->set_child(*scroller);
    return *popover;
 }
 // A video effect has nothing to do in a still, so it is offered only once the
 // project is a video.
 void EffectorWindow::updateVideoEffectItems() {
    for (auto* item : videoEffectItems_) item->set_sensitive(isVideo());
    if (videoEffectsHint_ != nullptr) videoEffectsHint_->set_visible(!isVideo());
 }
 void EffectorWindow::appendStage(const EffectPtr& effect) {
    stages_.push_back({effect, effect->defaults()});
    selectedStage_ = static_cast<int>(stages_.size()) - 1;
@@ -1782,7 +1833,8 @@ void EffectorWindow::rebuildChainRows() {
    // The first stage that actually runs is the one handed the sources, which
    // is not stage 1 once stage 1 is switched off.
-    const auto running = enabledStages(stages_);
+    const bool video = isVideo();
    const auto running = enabledStages(stages_, video);
    const int firstRunning =
        running.empty() ? -1 : static_cast<int>(running.front() - stages_.data());
@@ -1809,13 +1861,28 @@ void EffectorWindow::rebuildChainRows() {
        });
        box->append(*check);
        // A video effect is marked as one, and in a still it is dimmed like a
        // stage that is switched off: the render skips it either way.
        const bool videoEffect = stages_[i].effect->video();
        const bool skipped = !stages_[i].enabled || (videoEffect && !video);
        if (videoEffect) {
            auto* icon = Gtk::make_managed<Gtk::Image>(
                Gio::ThemedIcon::create("camera-video-symbolic"));
            icon->set_tooltip_text("A video effect");
            icon->set_margin_start(4);
            icon->set_margin_end(2);
            if (skipped) icon->add_css_class("dim-label");
            box->append(*icon);
        }
        auto* label = Gtk::make_managed<Gtk::Label>(stageLabel(i));
        stageLabels_.push_back(label);
        label->set_xalign(0.0F);
        label->set_hexpand(true);
        label->set_ellipsize(Pango::EllipsizeMode::END);
-        if (!stages_[i].enabled) label->add_css_class("dim-label");
+        if (skipped) label->add_css_class("dim-label");
-        label->set_tooltip_text(!stages_[i].enabled  ? "Skipped while it is switched off"
+        label->set_tooltip_text(!stages_[i].enabled ? "Skipped while it is switched off"
                                : skipped ? "A video effect: skipped in a still picture"
                                : index == firstRunning ? "Applied to the source images"
                                                        : "Applied to the output so far");
        box->append(*label);
@@ -2053,13 +2120,18 @@ void EffectorWindow::onRecreate() {
 // ever handed the sources, so an effect that does not want them (blur) renders
 // happily with none loaded.
 bool EffectorWindow::canRender() const {
-    if (enabledStages(stages_).empty()) return false;
+    if (enabledStages(stages_, isVideo()).empty()) return false;
-    return !sources_->empty() || !chainNeedsSources(stages_);
+    return !sources_->empty() || !chainNeedsSources(stages_, isVideo());
 }
 std::string EffectorWindow::missingText() const {
    if (stages_.empty()) return "Add an effect to start.";
-    if (enabledStages(stages_).empty()) return "Every effect is switched off.";
+    if (enabledStages(stages_, isVideo()).empty()) {
        if (!enabledStages(stages_, true).empty()) {
            return "Video effects run only in a video: switch on Video under Setup.";
        }
        return "Every effect is switched off.";
    }
    return "Add source images under Setup to start.";
 }
@@ -2203,7 +2275,7 @@ void EffectorWindow::onRenderFinished() {
    std::ostringstream status;
    status.setf(std::ios::fixed);
    status.precision(1);
-    const std::size_t effects = enabledStages(stages_).size();
+    const std::size_t effects = enabledStages(stages_, wasVideo).size();
    if (wasVideo) {
        result_ = Image();
        clip_ = std::move(incomingClip_);
@@ -2226,7 +2298,7 @@ void EffectorWindow::onRenderFinished() {
    // The line itself stays short; the full chain and setup go in the tooltip.
    std::ostringstream details;
-    details << chainTitle(stages_) << " · " << static_cast<int>(widthSpin_.get_value()) << "×"
+    details << chainTitle(stages_, wasVideo) << " · " << static_cast<int>(widthSpin_.get_value()) << "×"
            << static_cast<int>(heightSpin_.get_value()) << " · ";
    if (wasVideo) {
        const auto video = videoSettings();
@@ -2610,7 +2682,7 @@ void EffectorWindow::onSaveProjectAs() {
    dialog->set_title("Save project");
    dialog->set_filters(projectFilters());
    dialog->set_initial_name(projectPath_.empty()
-                                 ? "effector-" + chainSlug(stages_) + ".json"
+                                 ? "effector-" + chainSlug(stages_, isVideo()) + ".json"
                                 : std::filesystem::path(projectPath_).filename().string());
    dialog->save(*this, [this, dialog](const Glib::RefPtr<Gio::AsyncResult>& result) {
        onSaveProjectChosen(result, dialog);
@@ -2662,7 +2734,7 @@ void EffectorWindow::onSave() {
    auto dialog = Gtk::FileDialog::create();
    dialog->set_title(video ? "Save video" : "Save image");
-    dialog->set_initial_name("effector-" + chainSlug(stages_) + "-" + std::to_string(seed_) +
+    dialog->set_initial_name("effector-" + chainSlug(stages_, video) + "-" + std::to_string(seed_) +
                             (video ? ".mp4" : ".png"));
    dialog->save(*this, [this, dialog](const Glib::RefPtr<Gio::AsyncResult>& result) {
        onSaveChosen(result, dialog);
@@ -118,6 +118,7 @@ private:
    Gtk::Widget& buildChainSection();
    Gtk::Widget& buildAddMenu();      // the menu of effects that can be appended
    void updateVideoEffectItems();    // offers the video effects in a video only
    void appendStage(const EffectPtr& effect);
    void removeStage(int index);
    void moveStage(int from, int to);  // `to` is the index it ends up at
@@ -307,6 +308,10 @@ private:
    Gtk::Entry seedEntry_;
    Gtk::ListBox chainList_;
    Gtk::MenuButton addEffectButton_;
    // The entries of the video effects in its menu, and the line saying why
    // they cannot be picked in a still; both owned by the menu.
    std::vector<Gtk::Button*> videoEffectItems_;
    Gtk::Label* videoEffectsHint_ = nullptr;
    Gtk::MenuButton menuButton_;
    Gtk::Button recreateButton_{"Recreate"};
    Gtk::Button saveButton_{"Save As…"};
@@ -42,8 +42,8 @@ int renderVideo(const effector::Options& options, const std::vector<effector::Ch
    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
+              << effector::chainSlug(stages, true) << "  seed=" << seed << "  render="
-              << std::setprecision(1) << seconds << " s\n";
+              << std::fixed << std::setprecision(1) << seconds << " s\n";
    return 0;
 }
@@ -71,6 +71,17 @@ int renderHeadless(const effector::Options& options) {
        stages.push_back({effect, effect->defaults()});
    }
    // A video effect has nothing to do in a still; the render skips it, and
    // says so here rather than leave it looking forgotten.
    if (!options.video.enabled) {
        for (const auto& stage : stages) {
            if (!stage.enabled || !stage.effect->video()) continue;
            std::cerr << "effector: skipping " << stage.effect->name()
                      << ": a video effect, and this is a still (give --duration or "
                         "--video-preset for a clip)\n";
        }
    }
    std::vector<effector::LoadFailure> failures;
    // Decoding a batch of photographs takes seconds; on a terminal keep a
@@ -91,7 +102,7 @@ int renderHeadless(const effector::Options& options) {
    for (const auto& failure : failures) {
        std::cerr << "effector: skipping " << failure.path << ": " << failure.message << "\n";
    }
-    if (sources.empty() && effector::chainNeedsSources(stages)) {
+    if (sources.empty() && effector::chainNeedsSources(stages, options.video.enabled)) {
        std::cerr << "effector: no usable source images\n";
        return 2;
    }
@@ -108,7 +119,7 @@ int renderHeadless(const effector::Options& options) {
    image.save(options.output);
    std::cout << options.output << "  " << options.width << "x" << options.height
-              << "  effect=" << effector::chainSlug(stages) << "  seed=" << seed << "  render="
+              << "  effect=" << effector::chainSlug(stages, false) << "  seed=" << seed << "  render="
              << std::fixed << std::setprecision(1) << renderMillis << " ms\n";
    return 0;
 }
@@ -129,7 +140,8 @@ int main(int argc, char** argv) {
        }
        if (options.listEffects) {
            for (const auto& effect : effector::effects()) {
-                std::cout << effect->name() << "\t" << effect->title() << " - "
+                std::cout << effect->name() << "\t" << effect->title()
                          << (effect->video() ? " (video)" : "") << " - "
                          << effect->description() << "\n";
            }
            return 0;
@@ -35,6 +35,7 @@
 #include "effects/scanlines.hpp"
 #include "effects/text.hpp"
 #include "effects/tiles.hpp"
 #include "effects/video_effect.hpp"
 namespace {
@@ -1068,7 +1069,8 @@ int main() {
            check(sameBytes(renderChain({scanlines, stage}, sources, 300, 200, a),
                            renderChain({scanlines, stage}, sources, 300, 200, b)),
                  name + " cascades reproducibly");
-            check(!chainNeedsSources({stage, scanlines}), "a chain led by " + name + " needs no sources");
+            check(!chainNeedsSources({stage, scanlines}, false),
                  "a chain led by " + name + " needs no sources");
            // A canvas one pixel wide or high must not trip any of them up.
            check(renderNamed(name, {}, 1, 1, 2, {}).width() == 1 &&
@@ -1195,8 +1197,8 @@ int main() {
        const auto blurFirst = renderChain({blur, scanlines}, sources, 400, 300, backward);
        check(!sameBytes(blurLast, blurFirst), "the stage order changes the image");
-        check(chainTitle({scanlines, blur}) == "Scanlines \u2192 Blur", "the chain has a readable title");
+        check(chainTitle({scanlines, blur}, false) == "Scanlines \u2192 Blur", "the chain has a readable title");
-        check(chainSlug({scanlines, blur}) == "scanlines-blur", "the chain has a file name slug");
+        check(chainSlug({scanlines, blur}, false) == "scanlines-blur", "the chain has a file name slug");
        bool threw = false;
        try {
@@ -1211,10 +1213,10 @@ int main() {
        // them, blur only softens what it is handed and runs without any.
        check(effectByName("scanlines")->needsSources(), "scanlines needs source images");
        check(!effectByName("blur")->needsSources(), "blur needs no source images");
-        check(chainNeedsSources({scanlines, blur}), "a chain led by scanlines needs sources");
+        check(chainNeedsSources({scanlines, blur}, false), "a chain led by scanlines needs sources");
-        check(!chainNeedsSources({blur, scanlines}),
+        check(!chainNeedsSources({blur, scanlines}, false),
              "a chain led by blur needs none, later stages see the stage before them");
-        check(!chainNeedsSources({}), "an empty chain needs no sources");
+        check(!chainNeedsSources({}, false), "an empty chain needs no sources");
        Rng bare(5);
        const auto sourceless = renderChain({blur}, {}, 200, 150, bare);
@@ -1241,12 +1243,12 @@ int main() {
        Rng skipping(5);
        const auto skipped = renderChain({scanlines, blurOff}, sources, 400, 300, skipping);
        check(sameBytes(skipped, direct), "a disabled stage is skipped, its rng draws with it");
-        check(chainTitle({scanlines, blurOff}) == "Scanlines", "the title names only what ran");
+        check(chainTitle({scanlines, blurOff}, false) == "Scanlines", "the title names only what ran");
-        check(chainSlug({scanlines, blurOff}) == "scanlines", "and so does the slug");
+        check(chainSlug({scanlines, blurOff}, false) == "scanlines", "and so does the slug");
        // Whoever leads the chain is handed the sources, and that is the first
        // stage still switched on.
-        check(!chainNeedsSources({scanlinesOff, blur}),
+        check(!chainNeedsSources({scanlinesOff, blur}, false),
              "a disabled leading stage leaves the question to the stage behind it");
        Rng leading(5);
        const auto ledByBlur = renderChain({scanlinesOff, blur}, {}, 200, 150, leading);
@@ -1821,44 +1823,87 @@ int main() {
              "a video is recognised by its extension");
        const auto split = effector::effectByName("channelsplit");
        const auto tracking = effector::effectByName("tracking");
        const std::vector<effector::Image> sources = {gradient(96, 64, 40)};
-        // A still ignores every motion param: the picture is the one it
+        check(tracking->video() && !split->video(),
-        // always was, whatever they are set to.
+              "VHS tracking is a video effect, channel split an image one");
-        auto calm = split->defaults();
+        bool imagesFirst = true;
-        calm["split_mode"] = std::string("per_band");
+        bool seenVideo = false;
-        auto wild = calm;
+        for (const auto& effect : effects()) {
-        wild["split_wobble"] = 40L;
+            imagesFirst = imagesFirst && (effect->video() || !seenVideo);
-        wild["split_jitter"] = 30L;
+            seenVideo = seenVideo || effect->video();
-        wild["split_roll"] = 60L;
+        }
-        effector::Rng stillA(5);
+        check(imagesFirst, "the registry lists the image effects before the video effects");
        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 wild = tracking->defaults();
-        auto frozen = split->defaults();
+        wild["tracking_wobble"] = 40L;
-        frozen["split_wobble"] = 0L;
+        wild["tracking_jitter"] = 30L;
-        frozen["split_jitter"] = 0L;
+        wild["tracking_bar"] = 60L;
-        frozen["split_roll"] = 0L;
+        auto frozen = tracking->defaults();
-        check(!split->animated(frozen), "and holds still with every motion at 0");
+        frozen["tracking_wobble"] = 0L;
        frozen["tracking_jitter"] = 0L;
        frozen["tracking_bar"] = 0L;
-        // A moving stage leaves the shared rng in the same state on every
+        // A still skips a video effect whole, as it skips a stage switched
        // off: the picture is the one the chain made without it.
        ChainStage scanlinesStage{effectByName("scanlines"), {}};
        ChainStage trackingStage{tracking, wild};
        effector::Rng withRng(5);
        effector::Rng withoutRng(5);
        check(sameBytes(renderChain({scanlinesStage, trackingStage}, sources, 96, 64, withRng),
                        renderChain({scanlinesStage}, sources, 96, 64, withoutRng)),
              "a still skips a video effect as though it were not there");
        check(chainTitle({scanlinesStage, trackingStage}, false) == "Scanlines" &&
                  chainTitle({scanlinesStage, trackingStage}, true) == "Scanlines \u2192 VHS tracking",
              "and names it only in a video");
        check(chainNeedsSources({trackingStage, scanlinesStage}, false) &&
                  !chainNeedsSources({trackingStage, scanlinesStage}, true),
              "led by a video effect, a still starts from the stage after it");
        bool onlyVideo = false;
        try {
            effector::Rng rng(1);
            renderChain({trackingStage}, sources, 96, 64, rng);
        } catch (const EffectError&) {
            onlyVideo = true;
        }
        check(onlyVideo, "a still of video effects alone is refused");
        // A video effect 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});
+        tracking->renderFrame(sources, 96, 64, frameA, wild, FrameTime{3, 30, 30});
-        split->renderFrame(sources, 96, 64, frameB, wild, FrameTime{17, 30, 30});
+        tracking->renderFrame(sources, 96, 64, frameB, wild, FrameTime{17, 30, 30});
        check(frameA.next() == frameB.next(), "every frame leaves the shared rng in one state");
        // Time is rounded to fit the clip, so the frame after the last is the
        // first again, and a clip loops without a jump.
        const effector::Moment start(FrameTime{0, 30, 30}, 1);
        check(start.length() == 1.0 && start.loopRate(0.4) == 1.0 && start.loopRate(2.2) == 2.0,
              "a rate is rounded to a whole number of cycles in the clip");
        check(effector::Moment(FrameTime{15, 30, 30}, 1).cycle(1.0) == 0.5,
              "half-way through the clip is half-way through its one cycle");
        auto smooth = wild;
        smooth["tracking_jitter"] = 0L;
        const std::vector<effector::Image> input = {gradient(96, 64, 70)};
        effector::Rng loopA(4);
        effector::Rng loopB(4);
        check(sameBytes(tracking->renderFrame(input, 96, 64, loopA, smooth, FrameTime{0, 30, 30}),
                        tracking->renderFrame(input, 96, 64, loopB, smooth, FrameTime{30, 30, 30})),
              "without the shake, the clip loops without a jump");
        effector::Rng stillFrame(4);
        check(sameBytes(tracking->renderFrame(input, 96, 64, stillFrame, frozen, FrameTime{7, 30, 30}),
                        input[0]),
              "with every motion at 0 it leaves its input alone");
        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")};
+        std::vector<ChainStage> chain = {stage("tiles"), stage("tracking", wild), stage("grain")};
        VideoSettings video;
        video.enabled = true;
        video.duration = 1.0;
@@ -1896,7 +1941,7 @@ int main() {
        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<ChainStage> steady = {stage("tiles"), stage("channelsplit"), stage("grain")};
        std::vector<effector::Image> held;
        effector::renderFrames(steady, sources, 80, 48, 21, {}, video,
                               [&](int, effector::Image&& frame) {
@@ -1907,7 +1952,7 @@ int main() {
        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");
+              "a chain of image effects renders its still on every frame");
        int seen = 0;
        effector::renderFrames(chain, sources, 80, 48, 21, {}, video,
@@ -1931,7 +1976,7 @@ int main() {
        // The project file: a video says so, a still says nothing about time.
        effector::Project project;
-        project.stages = {stage("channelsplit", wild)};
+        project.stages = {stage("tracking", 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");
@@ -1944,8 +1989,8 @@ int main() {
                  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 &&
+        check(effector::paramInt(motion, "tracking_jitter", 0) == 30 &&
-                  effector::paramInt(motion, "split_roll", 0) == 60,
+                  effector::paramInt(motion, "tracking_bar", 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(),
@@ -109,6 +109,14 @@ Gtk::Button* menuEntry(Gtk::Popover& menu, const std::string& title) {
    return nullptr;
 }
 // Whether any label under `root` says `text`, shown or not.
 bool showsText(Gtk::Widget& root, const std::string& text) {
    for (auto* label : all<Gtk::Label>(root)) {
        if (label->get_text() == text) return true;
    }
    return false;
 }
 // Presses a button the way the keyboard does. GTK shows the press for a
 // quarter of a second before the button reports the click, so wait it out.
 void press(Gtk::Button& button) {
@@ -153,6 +161,11 @@ void dropStage(GtkDropTarget* drop, int index, double y) {
 void runTests(Gtk::Window& window) {
    const auto& effects = effector::effects();
    // What can be added to the still project the window opens on.
    std::vector<effector::EffectPtr> imageEffects;
    for (const auto& effect : effects) {
        if (!effect->video()) imageEffects.push_back(effect);
    }
    std::cout << "sidebar\n";
    auto* stack = all<Gtk::Stack>(window).empty() ? nullptr : all<Gtk::Stack>(window).front();
@@ -195,6 +208,19 @@ void runTests(Gtk::Window& window) {
    for (const auto& effect : effects) listed = listed && menuEntry(*menu, effect->title()) != nullptr;
    check(listed, "the menu has an entry for every registered effect");
    check(all<Gtk::Button>(*menu).size() == effects.size(), "and nothing else");
    bool offered = true;
    bool videoLast = true;
    bool seenVideo = false;
    for (const auto& effect : effects) {
        auto* entry = menuEntry(*menu, effect->title());
        offered = offered && entry->get_sensitive() != effect->video();
        videoLast = videoLast && (effect->video() || !seenVideo);
        seenVideo = seenVideo || effect->video();
    }
    check(seenVideo, "there is a video effect");
    check(videoLast && showsText(*menu, "Image effects") && showsText(*menu, "Video effects"),
          "the menu lists image effects and video effects under headings of their own");
    check(offered, "in a still project only the image effects can be picked");
    add->popup();
    pump();
@@ -204,12 +230,19 @@ void runTests(Gtk::Window& window) {
    // there were enough effects: the entries have to scroll instead, in a
    // menu short enough to open below a button near the top of a 768-pixel
    // screen.
    // Image and video effects scroll apart, so the video effects never
    // scroll out of sight below a long list of image effects.
    const auto scrollers = all<Gtk::ScrolledWindow>(*menu);
-    const int cap = scrollers.empty() ? -1 : scrollers.front()->get_max_content_height();
+    int cap = 0;
-    check(!scrollers.empty() && isAncestor(*scrollers.front(), *menuEntry(*menu, effects.front()->title())),
+    for (auto* scroller : scrollers) cap += scroller->get_max_content_height();
-          "the entries scroll");
+    bool scrolled = scrollers.size() == 2;
    for (const auto& effect : effects) {
        scrolled = scrolled &&
                   isAncestor(*scrollers[effect->video() ? 1 : 0], *menuEntry(*menu, effect->title()));
    }
    check(scrolled, "the image and the video entries scroll, each on their own");
    check(cap > 0 && cap <= 480, "past a height that fits a small screen");
-    check(menu->get_height() > 0 && menu->get_height() <= cap + 40,
+    check(menu->get_height() > 0 && menu->get_height() <= cap + 120,
          "and the menu stays within it however many effects there are");
    add->popdown();
    pump();
@@ -306,15 +339,19 @@ void runTests(Gtk::Window& window) {
    }
    std::cout << "many stages\n";
-    for (int i = 0; i < 4; ++i) addFromMenu(*add, effects[static_cast<std::size_t>(i) % effects.size()]->title());
+    for (int i = 0; i < 4; ++i) {
        addFromMenu(*add, imageEffects[static_cast<std::size_t>(i) % imageEffects.size()]->title());
    }
    pump();
    const int fewSplit = split != nullptr ? split->get_position() : -1;
    check(split != nullptr && fewSplit > emptySplit,
          "the split moves down as the chain grows");
-    for (int i = 4; i < 12; ++i) addFromMenu(*add, effects[static_cast<std::size_t>(i) % effects.size()]->title());
+    for (int i = 4; i < 12; ++i) {
        addFromMenu(*add, imageEffects[static_cast<std::size_t>(i) % imageEffects.size()]->title());
    }
    check(rowCount(*chainList) == 13, "the menu still works with a long chain");
-    check(addFromMenu(*add, effects.back()->title()) && rowCount(*chainList) == 14,
+    check(addFromMenu(*add, imageEffects.back()->title()) && rowCount(*chainList) == 14,
-          "including for the last effect in the menu");
+          "including for the last image effect in the menu");
    pump();
    const int longSplit = split != nullptr ? split->get_position() : -1;
    check(longSplit > fewSplit && listScroller != nullptr &&
@@ -455,7 +492,9 @@ void testVideo(Gtk::Window& window, const std::filesystem::path& dir) {
    std::filesystem::create_directories(dir);
    const auto path = dir / "moving.json";
    effector::Project project;
-    project.stages.push_back({effector::effectByName("channelsplit"), {}});  // needs no sources
+    // Neither needs sources: an image effect, then the video effect.
    project.stages.push_back({effector::effectByName("channelsplit"), {}});
    project.stages.push_back({effector::effectByName("tracking"), {}});
    effector::saveProject(path.string(), project);
    window.activate_action("win.open-recent",
                           Glib::Variant<Glib::ustring>::create(Glib::filename_to_uri(path.string())));
@@ -468,22 +507,49 @@ void testVideo(Gtk::Window& window, const std::filesystem::path& dir) {
    auto* width = named<Gtk::SpinButton>(window, "canvas-width");
    auto* height = named<Gtk::SpinButton>(window, "canvas-height");
    auto* playback = named<Gtk::Box>(window, "playback");
    auto* chainList = named<Gtk::ListBox>(window, "chain-list");
    auto* add = named<Gtk::MenuButton>(window, "add-effect");
    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) {
+        height == nullptr || playback == nullptr || chainList == nullptr || add == nullptr) {
        return;
    }
    const std::string tracking = effector::effectByName("tracking")->title();
    auto* entry = menuEntry(*add->get_popover(), tracking);
    // The label of a chain row, which says whether the stage runs.
    auto rowLabel = [&](int index) -> Gtk::Label* {
        auto* row = chainList->get_row_at_index(index);
        if (row == nullptr) return nullptr;
        for (auto* label : all<Gtk::Label>(*row)) {
            if (label->get_text().substr(0, 3) == std::to_string(index + 1) + ". ") return label;
        }
        return nullptr;
    };
    auto* videoRow = chainList->get_row_at_index(1);
    auto* videoLabel = rowLabel(1);
    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");
+    check(videoRow != nullptr && !all<Gtk::Image>(*videoRow).empty() && videoLabel != nullptr &&
              videoLabel->has_css_class("dim-label") &&
              videoLabel->get_tooltip_text() == "A video effect: skipped in a still picture",
          "a video stage is marked as one, and dimmed as skipped in a still");
    check(!rowLabel(0)->has_css_class("dim-label"), "while the image stage before it runs");
    check(entry != nullptr && !entry->get_sensitive(), "the video effect cannot be added to a still");
    toggle->set_active(true);
    pump(200);
    videoLabel = rowLabel(1);
    check(videoLabel != nullptr && !videoLabel->has_css_class("dim-label"),
          "in a video the video stage runs");
    check(entry != nullptr && entry->get_sensitive(), "and more can be added");
    chainList->select_row(*chainList->get_row_at_index(1));
    pump(100);
    check(showsLabel(window, "Wobble") && showsLabel(window, "Tracking bar"),
-          "a video shows the channel split's motion params");
+          "its settings are its motion");
    stack->set_visible_child("setup");
    pump(100);
    check(preset->is_drawable() && duration->is_drawable(), "and its preset and length");
@@ -511,8 +577,10 @@ void testVideo(Gtk::Window& window, const std::filesystem::path& dir) {
    toggle->set_active(false);
    pump(300);
-    check(!playback->get_visible() && !showsLabel(window, "Wobble"),
+    videoLabel = rowLabel(1);
-          "switched back to a still, the playback and motion params go");
+    check(!playback->get_visible() && videoLabel != nullptr &&
              videoLabel->has_css_class("dim-label") && entry != nullptr && !entry->get_sensitive(),
          "switched back to a still, the playback goes and the video stage is skipped again");
    stack->set_visible_child("chain");
 }