avformat/movenc: write the colr atom by default

The write_colr flag has been marked as experimental for over 5 years.
It should be safe to enable its behavior by default as follows:

  - Write the colr atom by default for mp4/mov if any of the following:
     - The primaries/trc/matrix are all specified, OR
     - There is an ICC profile, OR
     - The user specified +write_colr
  - Keep the write_colr flag for situations where the user wants to
    write the colr atom even if the color info is unspecified (e.g.,
    http://ffmpeg.org/pipermail/ffmpeg-devel/2020-March/259334.html)

This fixes https://trac.ffmpeg.org/ticket/7961

Signed-off-by: Michael Bradshaw <mjbshaw@google.com>

libavformat/movenc.c

@@ -78,7 +78,7 @@ static const AVOption options[] = {
     { "delay_moov", "Delay writing the initial moov until the first fragment is cut, or until the first fragment flush", 0, AV_OPT_TYPE_CONST, {.i64 = FF_MOV_FLAG_DELAY_MOOV}, INT_MIN, INT_MAX, AV_OPT_FLAG_ENCODING_PARAM, "movflags" },
     { "global_sidx", "Write a global sidx index at the start of the file", 0, AV_OPT_TYPE_CONST, {.i64 = FF_MOV_FLAG_GLOBAL_SIDX}, INT_MIN, INT_MAX, AV_OPT_FLAG_ENCODING_PARAM, "movflags" },
     { "skip_sidx", "Skip writing of sidx atom", 0, AV_OPT_TYPE_CONST, {.i64 = FF_MOV_FLAG_SKIP_SIDX}, INT_MIN, INT_MAX, AV_OPT_FLAG_ENCODING_PARAM, "movflags" },
-    { "write_colr", "Write colr atom (Experimental, may be renamed or changed, do not use from scripts)", 0, AV_OPT_TYPE_CONST, {.i64 = FF_MOV_FLAG_WRITE_COLR}, INT_MIN, INT_MAX, AV_OPT_FLAG_ENCODING_PARAM, "movflags" },
+    { "write_colr", "Write colr atom even if the color info is unspecified (Experimental, may be renamed or changed, do not use from scripts)", 0, AV_OPT_TYPE_CONST, {.i64 = FF_MOV_FLAG_WRITE_COLR}, INT_MIN, INT_MAX, AV_OPT_FLAG_ENCODING_PARAM, "movflags" },
     { "prefer_icc", "If writing colr atom prioritise usage of ICC profile if it exists in stream packet side data", 0, AV_OPT_TYPE_CONST, {.i64 = FF_MOV_FLAG_PREFER_ICC}, INT_MIN, INT_MAX, AV_OPT_FLAG_ENCODING_PARAM, "movflags" },
     { "write_gama", "Write deprecated gama atom", 0, AV_OPT_TYPE_CONST, {.i64 = FF_MOV_FLAG_WRITE_GAMA}, INT_MIN, INT_MAX, AV_OPT_FLAG_ENCODING_PARAM, "movflags" },
     { "use_metadata_tags", "Use mdta atom for metadata.", 0, AV_OPT_TYPE_CONST, {.i64 = FF_MOV_FLAG_USE_MDTA}, INT_MIN, INT_MAX, AV_OPT_FLAG_ENCODING_PARAM, "movflags" },
@@ -2164,11 +2164,17 @@ static int mov_write_video_tag(AVFormatContext *s, AVIOContext *pb, MOVMuxContex
         else
             av_log(mov->fc, AV_LOG_WARNING, "Not writing 'gama' atom. Format is not MOV.\n");
     }
-    if (mov->flags & FF_MOV_FLAG_WRITE_COLR) {
-        if (track->mode == MODE_MOV || track->mode == MODE_MP4)
-            mov_write_colr_tag(pb, track, mov->flags & FF_MOV_FLAG_PREFER_ICC);
-        else
-            av_log(mov->fc, AV_LOG_WARNING, "Not writing 'colr' atom. Format is not MOV or MP4.\n");
+    if (track->mode == MODE_MOV || track->mode == MODE_MP4) {
+        int has_color_info = track->par->color_primaries != AVCOL_PRI_UNSPECIFIED &&
+                             track->par->color_trc != AVCOL_TRC_UNSPECIFIED &&
+                             track->par->color_space != AVCOL_SPC_UNSPECIFIED;
+        if (has_color_info || mov->flags & FF_MOV_FLAG_WRITE_COLR ||
+            av_stream_get_side_data(track->st, AV_PKT_DATA_ICC_PROFILE, NULL)) {
+            int prefer_icc = mov->flags & FF_MOV_FLAG_PREFER_ICC || !has_color_info;
+            mov_write_colr_tag(pb, track, prefer_icc);
+        } else if (mov->flags & FF_MOV_FLAG_WRITE_COLR) {
+             av_log(mov->fc, AV_LOG_WARNING, "Not writing 'colr' atom. Format is not MOV or MP4.\n");
+        }
     }
     if (track->mode == MODE_MOV || track->mode == MODE_MP4) {
         mov_write_clli_tag(pb, track);

tests/ref/fate/copy-trac236

@@ -1,5 +1,5 @@
-984a33c6292e3d35e2cfdfbf66d8e82b *tests/data/fate/copy-trac236.mov
-630860 tests/data/fate/copy-trac236.mov
+34b0ad38518b0eb8464aff04e6d0e143 *tests/data/fate/copy-trac236.mov
+630878 tests/data/fate/copy-trac236.mov
 #tb 0: 100/2997
 #media_type 0: video
 #codec_id 0: rawvideo