Relay picks the most compact video codec (HEVC, AV1, VP9, then h264)

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

docs/ARCHITECTURE.md

@@ -512,8 +512,9 @@ all three link modes. Nothing is bundled or installed by hand.
   - the best single file (`pickSingleFile`: video and audio not `none`, a
     video container, tallest up to 1080p, else the shortest above), unless
   - a video-only + audio-only pair is taller (`pickSplit`): video tallest
-    up to 1080p (else the shortest above), avc1 before vp9 before av01
-    (hardware decoding), then bitrate; audio the original language, not a
+    up to 1080p (else the shortest above), HEVC before AV1 before VP9
+    before h264 (the most compact first: relayed bytes cost every viewer
+    and the server buffer, and mpv decodes them all), then bitrate; audio the original language, not a
     `-drc` variant unless alone, m4a/aac before opus, then bitrate.
     YouTube has only these (299 + 140 for a 1080p60 video).
   - Neither (only HLS/DASH playlists) or a live stream: nothing to relay.

packages/core/lib/src/yt_dlp.dart

@@ -161,18 +161,23 @@ YtDlpFormat? pickSingleFile(List<Object?> formats, {int maxHeight = 1080}) {
   return YtDlpFormat._of(ok.first);
 }
 
+// Relayed bytes cost every viewer bandwidth and the server buffer, and mpv
+// decodes all of these: the most compact codec first. HEVC (hardware
+// decoding nearly everywhere), then AV1 (smallest; software is fine to
+// 1080p), then VP9, then h264.
 int _videoCodecRank(Map f) {
   final c = '${f['vcodec']}'.toLowerCase();
-  if (c.startsWith('avc') || c.startsWith('h264')) return 0;
-  if (c.startsWith('vp9') || c.startsWith('vp09')) return 1;
-  if (c.startsWith('av01')) return 2;
-  return 3;
+  if (c.startsWith('hvc') || c.startsWith('hev') || c.startsWith('h265')) return 0;
+  if (c.startsWith('av01')) return 1;
+  if (c.startsWith('vp9') || c.startsWith('vp09')) return 2;
+  if (c.startsWith('avc') || c.startsWith('h264')) return 3;
+  return 4;
 }
 
 /// The best video-only + audio-only pair of plain http(s) files (YouTube's
 /// DASH formats), or null. Video: the tallest up to [maxHeight] (else the
-/// shortest above), avc1 before vp9 before av01 (hardware decoding), then
-/// bitrate. Audio: the original language, not a `-drc` variant, m4a/aac
+/// shortest above), HEVC before AV1 before VP9 before h264 (smallest
+/// first, see [_videoCodecRank]), then bitrate. Audio: the original language, not a `-drc` variant, m4a/aac
 /// before others (opus), then bitrate.
 (YtDlpFormat, YtDlpFormat)? pickSplit(List<Object?> formats, {int maxHeight = 1080}) {
   final video = [

packages/core/test/yt_dlp_test.dart

@@ -90,10 +90,10 @@ void main() {
       _f('96', 'm3u8_native', 'avc1', 'mp4a', 1080),
     ];
 
-    test('YouTube: avc1 video up to 1080p (highest bitrate) + m4a audio, with the chunk size', () {
+    test('YouTube: the most compact codec up to 1080p (VP9 over h264 here) + m4a audio, with the chunk size', () {
       final t = pickTracks(youtube);
-      expect([for (final x in t) (x.kind, x.format.id)], [('video', '299'), ('audio', '140')]);
-      expect(t.first.format.chunkSize, 10485760);
+      expect([for (final x in t) (x.kind, x.format.id)], [('video', '248'), ('audio', '140')]);
+      expect(YtDlpInfo.parse({'title': 'x', 'formats': youtube}).formats['299']?.chunkSize, 10485760);
       expect(YtDlpInfo.parse({'title': 'x', 'formats': youtube}).formats['137']?.height, 1080);
     });
 
@@ -200,4 +200,15 @@ void main() {
     await media.close();
     expect(n, size);
   }, timeout: const Timeout(Duration(minutes: 3)), skip: Platform.environment['YTDLP_LIVE'] == '1' ? false : 'YTDLP_LIVE not set');
+
+  test('codec order: HEVC, then AV1, then VP9, then h264 at the same height', () {
+    final audio = _f('140', 'https', 'none', 'mp4a.40.2', null);
+    String pick(List<String> codecs) => pickSplit([
+          for (final (i, c) in codecs.indexed) _f('v$i', 'https', c, 'none', 1080),
+          audio,
+        ])!.$1.id;
+    expect(pick(['avc1.640033', 'vp09.00.40.08', 'av01.0.08M.08', 'hvc1.1.6.L12']), 'v3');
+    expect(pick(['avc1.640033', 'vp09.00.40.08', 'av01.0.08M.08']), 'v2');
+    expect(pick(['avc1.640033', 'vp09.00.40.08']), 'v1');
+  });
 }