matroskadec: export cover art correctly

Generally, libavformat exports cover art pictures as video streams with
1 packet and AV_DISPOSITION_ATTACHED_PIC set. Only matroskadec exported
it as attachment with codec_id set to AV_CODEC_ID_MJPEG.

Obviously, this should be consistent, so change the Matroska demuxer to
export a AV_DISPOSITION_ATTACHED_PIC pseudo video stream.

Matroska muxing is probably incorrect too. I know that it can create
broken files with an audio track and just 1 video frame when e.g.
remuxing mp3 with APIC to mkv. But for now this commit does not change
anything about muxing, and also continues to write attachments with
AV_CODEC_ID_MJPEG should the muxer application have special knowledge
that the Matroska is broken in this way.

Signed-off-by: Anton Khirnov <anton@khirnov.net>

1 files changed, 1 insertions, 0 deletions

diff --git a/libavformat/matroska.h b/libavformat/matroska.h
index d8f4f8ebec..a7a22a96af 100644
--- a/libavformat/matroska.h
+++ b/libavformat/matroska.h
@@ -254,6 +254,7 @@ typedef struct CodecTags{
 
 extern const CodecTags ff_mkv_codec_tags[];
 extern const CodecMime ff_mkv_mime_tags[];
+extern const CodecMime ff_mkv_image_mime_tags[];
 extern const AVMetadataConv ff_mkv_metadata_conv[];
 
 int ff_mkv_stereo3d_conv(AVStream *st, MatroskaVideoStereoModeType stereo_mode);