avformat/matroskaenc: Allow to set multiple streams as default

The Matroska specifications have evolved and now allow to mark
multiple tracks of the same kind as default (whether this was legal or
not before was dubious; e.g. mkvmerge disallowed it). Yet when the
Matroska muxer is set to infer default dispositions if absent, it also
enforced the now outdated restriction. So update this.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

3 files changed, 14 insertions, 18 deletions

diff --git a/doc/muxers.texi b/doc/muxers.texi
index 0972bbfd5c..0f8efabab9 100644
--- a/doc/muxers.texi
+++ b/doc/muxers.texi
@@ -1567,12 +1567,12 @@ It influences which tracks players should play by default. The default mode
 is @samp{infer}.
 @table @samp
 @item infer
-In this mode, for each type of track (audio, video or subtitle), if there is
-a track with disposition default of this type, then the first such track
-(i.e. the one with the lowest index) will be marked as default; if no such
-track exists, the first track of this type will be marked as default instead
-(if existing). This ensures that the default flag is set in a sensible way even
-if the input originated from containers that lack the concept of default tracks.
+Every track with disposition default will have the FlagDefault set.
+Additionally, for each type of track (audio, video or subtitle), if no track
+with disposition default of this type exists, then the first track of this type
+will be marked as default (if existing). This ensures that the default flag
+is set in a sensible way even if the input originated from containers that
+lack the concept of default tracks.
 @item infer_no_subs
 This mode is the same as infer except that if no subtitle track with
 disposition default exists, no subtitle track will be marked as default.
diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c
index 899a3388cd..e2d9159e2c 100644
--- a/libavformat/matroskaenc.c
+++ b/libavformat/matroskaenc.c
@@ -1395,7 +1395,8 @@ static int mkv_write_tracks(AVFormatContext *s)
 {
     MatroskaMuxContext *mkv = s->priv_data;
     AVIOContext *pb = s->pb;
-    int i, ret, video_default_idx, audio_default_idx, subtitle_default_idx;
+    int video_default_idx = -1, audio_default_idx = -1, subtitle_default_idx = -1;
+    int i, ret;
 
     if (mkv->nb_attachments == s->nb_streams)
         return 0;
@@ -1405,11 +1406,7 @@ static int mkv_write_tracks(AVFormatContext *s)
         return ret;
 
     if (mkv->default_mode != DEFAULT_MODE_PASSTHROUGH) {
-        int video_idx, audio_idx, subtitle_idx;
-
-        video_idx    = video_default_idx    =
-        audio_idx    = audio_default_idx    =
-        subtitle_idx = subtitle_default_idx = -1;
+        int video_idx = -1, audio_idx = -1, subtitle_idx = -1;
 
         for (i = s->nb_streams - 1; i >= 0; i--) {
             AVStream *st = s->streams[i];
@@ -1435,8 +1432,7 @@ static int mkv_write_tracks(AVFormatContext *s)
     }
     for (i = 0; i < s->nb_streams; i++) {
         AVStream *st = s->streams[i];
-        int is_default = mkv->default_mode == DEFAULT_MODE_PASSTHROUGH ?
-                             st->disposition & AV_DISPOSITION_DEFAULT  :
+        int is_default = st->disposition & AV_DISPOSITION_DEFAULT ||
                              i == video_default_idx || i == audio_default_idx ||
                              i == subtitle_default_idx;
         ret = mkv_write_track(s, mkv, st, &mkv->tracks[i],
@@ -2823,8 +2819,8 @@ static const AVOption options[] = {
     { "flipped_raw_rgb", "Raw RGB bitmaps in VFW mode are stored bottom-up", OFFSET(flipped_raw_rgb), AV_OPT_TYPE_BOOL, { .i64 = 0 }, 0, 1, FLAGS },
     { "write_crc32", "write a CRC32 element inside every Level 1 element", OFFSET(write_crc), AV_OPT_TYPE_BOOL, { .i64 = 1 }, 0, 1, FLAGS },
     { "default_mode", "Controls how a track's FlagDefault is inferred", OFFSET(default_mode), AV_OPT_TYPE_INT, { .i64 = DEFAULT_MODE_INFER }, DEFAULT_MODE_INFER, DEFAULT_MODE_PASSTHROUGH, FLAGS, "default_mode" },
-    { "infer", "For each track type, mark the first track of disposition default as default; if none exists, mark the first track as default.", 0, AV_OPT_TYPE_CONST, { .i64 = DEFAULT_MODE_INFER }, 0, 0, FLAGS, "default_mode" },
-    { "infer_no_subs", "For each track type, mark the first track of disposition default as default; for audio and video: if none exists, mark the first track as default.", 0, AV_OPT_TYPE_CONST, { .i64 = DEFAULT_MODE_INFER_NO_SUBS }, 0, 0, FLAGS, "default_mode" },
+    { "infer", "For each track type, mark each track of disposition default as default; if none exists, mark the first track as default.", 0, AV_OPT_TYPE_CONST, { .i64 = DEFAULT_MODE_INFER }, 0, 0, FLAGS, "default_mode" },
+    { "infer_no_subs", "For each track type, mark each track of disposition default as default; for audio and video: if none exists, mark the first track as default.", 0, AV_OPT_TYPE_CONST, { .i64 = DEFAULT_MODE_INFER_NO_SUBS }, 0, 0, FLAGS, "default_mode" },
     { "passthrough", "Use the disposition flag as-is", 0, AV_OPT_TYPE_CONST, { .i64 = DEFAULT_MODE_PASSTHROUGH }, 0, 0, FLAGS, "default_mode" },
     { NULL },
 };
diff --git a/tests/ref/fate/matroska-flac-extradata-update b/tests/ref/fate/matroska-flac-extradata-update
index fb17bfea0b..1a8add7736 100644
--- a/tests/ref/fate/matroska-flac-extradata-update
+++ b/tests/ref/fate/matroska-flac-extradata-update
@@ -1,5 +1,5 @@
-3c721898cf2cf3e2e6c43ad58952bd2d *tests/data/fate/matroska-flac-extradata-update.matroska
-2032 tests/data/fate/matroska-flac-extradata-update.matroska
+c2b76d47a9f0e9626a4999bd395cae08 *tests/data/fate/matroska-flac-extradata-update.matroska
+2029 tests/data/fate/matroska-flac-extradata-update.matroska
 #extradata 0:       34, 0x7acb09e7
 #extradata 1:       34, 0x7acb09e7
 #extradata 2:       34, 0x443402dd