[FFmpeg-devel] [PATCH/RFC]av_codec_get_tag() cannot work for Matroska (Ticket 8)

[Carl Eugen Hoyos]

Hi!

ffmpeg.c sets codec_tag for the output stream in the stream copy case if 
codec_tag was set by the demuxer, and no default codec_tag for the codec can 
be found in the muxers' list of codec_tags using av_codec_get_tag (and also if 
no such list was defined and also if the codec_tag is known to be correct).
(line 2231 - 2235)

The ts demuxer always sets codec_tag, it was discussed here before that this 
is intended (third party applications may like the value).

Matroska cannot provide a codec_tags list compatible with av_codec_get_tag and 
therefore provides the wav (and the bmp) list.

Some codecs that work in Matroska are not listed in the wav (and bmp) list, 
making stream copy impossible if a codec_tag was set because the set codec_tag 
is rejected later (it is for example not set for TrueHD, so it is possible 
that only the EAC3 in ts case - at least for some samples - triggers) in 
avformat_write_header() / validate_codec_tag().

Attached is a try to fix this by adding the missing audio codec_tags (I will 
do similar for subtitles and video if needed), I would be glad if a simpler 
solution is possible like not to try to validate the codec_tag for matroska.

Carl Eugen
-------------- next part --------------
diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c
index 0910da5..0bc995f 100644
--- a/libavformat/matroskaenc.c
+++ b/libavformat/matroskaenc.c
@@ -1214,6 +1214,25 @@ static int mkv_query_codec(enum CodecID codec_id, int std_compliance)
     return 0;
 }
 
+/* The following tags are not listed in ff_codec_wav_tags,
+ * so av_codec_get_id() and av_codec_get_tag() would incorrectly fail
+ * if they are not listed here. */
+const AVCodecTag missing_audio_tags[] = {
+    { CODEC_ID_EAC3,      0xFFFFFFFF },
+    { CODEC_ID_MLP,       0xFFFFFFFF },
+    { CODEC_ID_PCM_S16BE, 0xFFFFFFFF },
+    { CODEC_ID_PCM_S24BE, 0xFFFFFFFF },
+    { CODEC_ID_PCM_S32BE, 0xFFFFFFFF },
+    { CODEC_ID_QDM2,      0xFFFFFFFF },
+    { CODEC_ID_RA_144,    0xFFFFFFFF },
+    { CODEC_ID_RA_288,    0xFFFFFFFF },
+    { CODEC_ID_COOK,      0xFFFFFFFF },
+    { CODEC_ID_TRUEHD,    0xFFFFFFFF },
+    { CODEC_ID_TTA,       0xFFFFFFFF },
+    { CODEC_ID_WAVPACK,   0xFFFFFFFF },
+    { CODEC_ID_NONE,      0xFFFFFFFF }
+};
+
 #if CONFIG_MATROSKA_MUXER
 AVOutputFormat ff_matroska_muxer = {
     .name              = "matroska",
@@ -1235,7 +1254,7 @@ AVOutputFormat ff_matroska_muxer = {
     .write_packet      = mkv_write_packet,
     .write_trailer     = mkv_write_trailer,
     .flags             = AVFMT_GLOBALHEADER | AVFMT_VARIABLE_FPS,
-    .codec_tag         = (const AVCodecTag* const []){ff_codec_bmp_tags, ff_codec_wav_tags, 0},
+    .codec_tag         = (const AVCodecTag* const []){ff_codec_bmp_tags, ff_codec_wav_tags, missing_audio_tags, 0},
     .subtitle_codec    = CODEC_ID_SSA,
     .query_codec       = mkv_query_codec,
 };
@@ -1274,6 +1293,6 @@ AVOutputFormat ff_matroska_audio_muxer = {
     .write_packet      = mkv_write_packet,
     .write_trailer     = mkv_write_trailer,
     .flags = AVFMT_GLOBALHEADER,
-    .codec_tag = (const AVCodecTag* const []){ff_codec_wav_tags, 0},
+    .codec_tag = (const AVCodecTag* const []){ff_codec_wav_tags, missing_audio_tags, 0},
 };
 #endif
-------------- next part --------------
diff --git a/libavformat/utils.c b/libavformat/utils.c
index ef1de94..8fac96e 100644
--- a/libavformat/utils.c
+++ b/libavformat/utils.c
@@ -2986,7 +2986,7 @@ int avformat_write_header(AVFormatContext *s, AVDictionary **options)
             break;
         }
 
-        if(s->oformat->codec_tag){
+        if(s->oformat->codec_tag && strcmp(s->oformat->name, "matroska")){
             if(st->codec->codec_tag && st->codec->codec_id == CODEC_ID_RAWVIDEO && av_codec_get_tag(s->oformat->codec_tag, st->codec->codec_id) == 0 && !validate_codec_tag(s, st)){
                 //the current rawvideo encoding system ends up setting the wrong codec_tag for avi, we override it here
                 st->codec->codec_tag= 0;