Add a video export quality choice: Small file, Standard or High

A Quality dropdown under Video on Setup, --video-quality on the command
line, and "quality" in a project's video settings (written only when it is
not Standard). One table, videoQualities(), holds the ffmpeg settings per
codec; Standard is what every video was written with before.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/core/video.cpp

@@ -51,6 +51,31 @@ const VideoPreset* videoPresetByKey(const std::string& key) {
     return nullptr;
 }
 
+const std::vector<VideoQuality>& videoQualities() {
+    // Standard is what every video was written with before there was a
+    // choice: CRF 18 is close to what the eye can tell from the frames.
+    static const std::vector<VideoQuality> qualities = {
+        {"small", "Small file", "smaller and quicker to share, with visible softening", 26, "fast",
+         40, 128},
+        {kDefaultVideoQuality, "Standard", "close to the rendered frames at a moderate size", 18,
+         "medium", 32, 256},
+        {"high", "High", "as faithful as it gets, larger and slower to write", 12, "slow", 24, 256},
+    };
+    return qualities;
+}
+
+const VideoQuality* videoQualityByKey(const std::string& key) {
+    for (const auto& quality : videoQualities()) {
+        if (quality.key == key) return &quality;
+    }
+    return nullptr;
+}
+
+const VideoQuality& videoQualityOrDefault(const std::string& key) {
+    if (const auto* quality = videoQualityByKey(key)) return *quality;
+    return *videoQualityByKey(kDefaultVideoQuality);
+}
+
 // 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) {
@@ -106,7 +131,8 @@ bool ffmpegAvailable() {
     return false;
 }
 
-VideoWriter::VideoWriter(const std::string& path, int width, int height, int fps)
+VideoWriter::VideoWriter(const std::string& path, int width, int height, int fps,
+                         const std::string& quality)
     : path_(path), width_(width), height_(height) {
     const std::string muxer = muxerFor(lowerExtension(path));
     if (muxer.empty()) {
@@ -120,6 +146,7 @@ VideoWriter::VideoWriter(const std::string& path, int width, int height, int fps
     static std::once_flag ignorePipe;
     std::call_once(ignorePipe, [] { ::signal(SIGPIPE, SIG_IGN); });
 
+    const VideoQuality& squeeze = videoQualityOrDefault(quality);
     std::vector<std::string> args = {
         "ffmpeg", "-hide_banner", "-loglevel", "error", "-y",
         "-f", "rawvideo", "-pix_fmt", "rgb24",
@@ -129,16 +156,20 @@ VideoWriter::VideoWriter(const std::string& path, int width, int height, int fps
     };
     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",
+        args.insert(args.end(), {"-vf", "split[a][b];[b]palettegen=max_colors=" +
+                                           std::to_string(squeeze.gifColors) +
+                                           "[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",
+            args.insert(args.end(), {"-c:v", "libvpx-vp9", "-crf", std::to_string(squeeze.vp9Crf),
+                                     "-b:v", "0",
                                      "-row-mt", "1"});
         } else {
-            args.insert(args.end(), {"-c:v", "libx264", "-preset", "medium", "-crf", "18"});
+            args.insert(args.end(), {"-c:v", "libx264", "-preset", squeeze.h264Preset, "-crf",
+                                     std::to_string(squeeze.h264Crf)});
         }
         args.insert(args.end(), {"-pix_fmt", "yuv420p"});
         if (muxer == "mp4" || muxer == "mov") args.insert(args.end(), {"-movflags", "+faststart"});