avformat/matroskadec: Add support for FlagOriginal

Needs a CountedElement in order to distinguish the case of the element
not being present and the element being present with a value of zero.

(It has been argued by Ridley Combs that one should only ever use the
AV_DISPOSITION_DUB field for audio tracks. Yet given that there is no
definition for the disposition flags, one can also interpret it to mean
that e.g. a subtitle track is meant to be used with the dubbed audio
track or the original audio track. This commit interprets this flag in
this sense, which also allows to maintain it on remuxing.)

Reviewed-by: Anton Khirnov <anton@khirnov.net>
Reviewed-by: Ridley Combs <rcombs@rcombs.me>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavformat/matroska.h

@@ -101,6 +101,7 @@
 #define MATROSKA_ID_TRACKFLAGHEARINGIMPAIRED  0x55AB
 #define MATROSKA_ID_TRACKFLAGVISUALIMPAIRED   0x55AC
 #define MATROSKA_ID_TRACKFLAGTEXTDESCRIPTIONS 0x55AD
+#define MATROSKA_ID_TRACKFLAGORIGINAL         0x55AE
 #define MATROSKA_ID_TRACKFLAGCOMMENTARY       0x55AF
 #define MATROSKA_ID_TRACKFLAGLACING 0x9C
 #define MATROSKA_ID_TRACKMINCACHE 0x6DE7

libavformat/matroskadec.c

@@ -254,6 +254,7 @@ typedef struct MatroskaTrack {
     uint64_t flag_hearingimpaired;
     uint64_t flag_visualimpaired;
     uint64_t flag_textdescriptions;
+    CountedElement flag_original;
     uint64_t seek_preroll;
     MatroskaTrackVideo video;
     MatroskaTrackAudio audio;
@@ -413,7 +414,7 @@ typedef struct MatroskaDemuxContext {
 // incomplete type (6.7.2 in C90, 6.9.2 in C99).
 // Removing the sizes breaks MSVC.
 static EbmlSyntax ebml_syntax[3], matroska_segment[9], matroska_track_video_color[15], matroska_track_video[19],
-                  matroska_track[31], matroska_track_encoding[6], matroska_track_encodings[2],
+                  matroska_track[32], matroska_track_encoding[6], matroska_track_encodings[2],
                   matroska_track_combine_planes[2], matroska_track_operation[2], matroska_tracks[2],
                   matroska_attachments[2], matroska_chapter_entry[9], matroska_chapter[6], matroska_chapters[2],
                   matroska_index_entry[3], matroska_index[2], matroska_tag[3], matroska_tags[2], matroska_seekhead[2],
@@ -581,6 +582,7 @@ static EbmlSyntax matroska_track[] = {
     { MATROSKA_ID_TRACKFLAGHEARINGIMPAIRED, EBML_UINT, 0, 0, offsetof(MatroskaTrack, flag_hearingimpaired), { .u = 0 } },
     { MATROSKA_ID_TRACKFLAGVISUALIMPAIRED, EBML_UINT, 0, 0, offsetof(MatroskaTrack, flag_visualimpaired), { .u = 0 } },
     { MATROSKA_ID_TRACKFLAGTEXTDESCRIPTIONS, EBML_UINT, 0, 0, offsetof(MatroskaTrack, flag_textdescriptions), { .u = 0 } },
+    { MATROSKA_ID_TRACKFLAGORIGINAL,     EBML_UINT,  1, 0, offsetof(MatroskaTrack, flag_original), {.u = 0 } },
     { MATROSKA_ID_TRACKVIDEO,            EBML_NEST,  0, 0, offsetof(MatroskaTrack, video),        { .n = matroska_track_video } },
     { MATROSKA_ID_TRACKAUDIO,            EBML_NEST,  0, 0, offsetof(MatroskaTrack, audio),        { .n = matroska_track_audio } },
     { MATROSKA_ID_TRACKOPERATION,        EBML_NEST,  0, 0, offsetof(MatroskaTrack, operation),    { .n = matroska_track_operation } },
@@ -2755,6 +2757,9 @@ static int matroska_parse_tracks(AVFormatContext *s)
             st->disposition |= AV_DISPOSITION_HEARING_IMPAIRED;
         if (track->flag_visualimpaired)
             st->disposition |= AV_DISPOSITION_VISUAL_IMPAIRED;
+        if (track->flag_original.count > 0)
+            st->disposition |= track->flag_original.el.u ? AV_DISPOSITION_ORIGINAL
+                                                         : AV_DISPOSITION_DUB;
 
         if (!st->codecpar->extradata) {
             if (extradata) {