avformat/matroskaenc: Redo handling of FlagDefault

Up until now, the Matroska muxer would mark a track as default if it had
the disposition AV_DISPOSITION_DEFAULT or if there was no track with
AV_DISPOSITION_DEFAULT set; in the latter case even more than one track
of a kind (audio, video, subtitles) was marked as default which is not
sensible.

This commit changes the logic used to mark tracks as default. There are
now three modes for this:
a) In the "infer" mode the first track of every type (audio, video,
subtitles) with default disposition set will be marked as default; if
there is no such track (for a given type), then the first track of this
type (if existing) will be marked as default. This behaviour is inspired
by mkvmerge. It ensures that the default flags will be set in a sensible
way even if the input comes from containers that lack the concept of
default flags. This mode is the default mode.
b) The "infer_no_subs" mode is similar to the "infer" mode; the
difference is that if no subtitle track with default disposition exists,
no subtitle track will be marked as default at all.
c) The "passthrough" mode: Here the track will be marked as default if
and only the corresponding input stream had disposition default.

This fixes ticket #8173 (the passthrough mode is ideal for this) as
well as ticket #8416 (the "infer_no_subs" mode leads to the desired
output).

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

1 files changed, 48 insertions, 8 deletions

diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c
index 71b6b6cc91..b7b6e9fbc0 100644
--- a/libavformat/matroskaenc.c
+++ b/libavformat/matroskaenc.c
@@ -58,6 +58,12 @@
  * Info, Tracks, Chapters, Attachments, Tags and Cues */
 #define MAX_SEEKHEAD_ENTRIES 6
 
+enum {
+    DEFAULT_MODE_INFER,
+    DEFAULT_MODE_INFER_NO_SUBS,
+    DEFAULT_MODE_PASSTHROUGH,
+};
+
 typedef struct ebml_master {
     int64_t         pos;                ///< absolute offset in the containing AVIOContext where the master's elements start
     int             sizebytes;          ///< how many bytes were reserved for the size
@@ -144,6 +150,7 @@ typedef struct MatroskaMuxContext {
     int wrote_chapters;
 
     int allow_raw_vfw;
+    int default_mode;
 
     uint32_t segment_uid[4];
 } MatroskaMuxContext;
@@ -1102,7 +1109,7 @@ static int mkv_write_stereo_mode(AVFormatContext *s, AVIOContext *pb,
 
 static int mkv_write_track(AVFormatContext *s, MatroskaMuxContext *mkv,
                            AVStream *st, mkv_track *track, AVIOContext *pb,
-                           int default_stream_exists)
+                           int is_default)
 {
     AVCodecParameters *par = st->codecpar;
     ebml_master subinfo, track_master;
@@ -1140,8 +1147,8 @@ static int mkv_write_track(AVFormatContext *s, MatroskaMuxContext *mkv,
 
     // The default value for TRACKFLAGDEFAULT is 1, so add element
     // if we need to clear it.
-    if (default_stream_exists && !(st->disposition & AV_DISPOSITION_DEFAULT))
-        put_ebml_uint(pb, MATROSKA_ID_TRACKFLAGDEFAULT, !!(st->disposition & AV_DISPOSITION_DEFAULT));
+    if (!is_default)
+        put_ebml_uint(pb, MATROSKA_ID_TRACKFLAGDEFAULT, 0);
 
     if (st->disposition & AV_DISPOSITION_FORCED)
         put_ebml_uint(pb, MATROSKA_ID_TRACKFLAGFORCED, 1);
@@ -1371,7 +1378,7 @@ static int mkv_write_tracks(AVFormatContext *s)
 {
     MatroskaMuxContext *mkv = s->priv_data;
     AVIOContext *pb = s->pb;
-    int i, ret, default_stream_exists = 0;
+    int i, ret, video_default_idx, audio_default_idx, subtitle_default_idx;
 
     if (mkv->nb_attachments == s->nb_streams)
         return 0;
@@ -1382,14 +1389,43 @@ static int mkv_write_tracks(AVFormatContext *s)
     if (ret < 0)
         return ret;
 
-    for (i = 0; i < s->nb_streams; i++) {
-        AVStream *st = s->streams[i];
-        default_stream_exists |= st->disposition & AV_DISPOSITION_DEFAULT;
+    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;
+
+        for (i = s->nb_streams - 1; i >= 0; i--) {
+            AVStream *st = s->streams[i];
+
+            switch (st->codecpar->codec_type) {
+#define CASE(type, variable)                                  \
+            case AVMEDIA_TYPE_ ## type:                       \
+                variable ## _idx = i;                         \
+                if (st->disposition & AV_DISPOSITION_DEFAULT) \
+                    variable ## _default_idx = i;             \
+                break;
+            CASE(VIDEO,    video)
+            CASE(AUDIO,    audio)
+            CASE(SUBTITLE, subtitle)
+#undef CASE
+            }
+        }
+
+        video_default_idx = FFMAX(video_default_idx, video_idx);
+        audio_default_idx = FFMAX(audio_default_idx, audio_idx);
+        if (mkv->default_mode != DEFAULT_MODE_INFER_NO_SUBS)
+            subtitle_default_idx = FFMAX(subtitle_default_idx, subtitle_idx);
     }
     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  :
+                             i == video_default_idx || i == audio_default_idx ||
+                             i == subtitle_default_idx;
         ret = mkv_write_track(s, mkv, st, &mkv->tracks[i],
-                              mkv->tracks_bc, default_stream_exists);
+                              mkv->tracks_bc, is_default);
         if (ret < 0)
             return ret;
     }
@@ -2722,6 +2758,10 @@ static const AVOption options[] = {
     { "live", "Write files assuming it is a live stream.", OFFSET(is_live), AV_OPT_TYPE_BOOL, { .i64 = 0 }, 0, 1, FLAGS },
     { "allow_raw_vfw", "allow RAW VFW mode", OFFSET(allow_raw_vfw), 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" },
+    { "passthrough", "Use the disposition flag as-is", 0, AV_OPT_TYPE_CONST, { .i64 = DEFAULT_MODE_PASSTHROUGH }, 0, 0, FLAGS, "default_mode" },
     { NULL },
 };