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

Michael Niedermayer michaelni at gmx.at
Thu Aug 25 00:03:13 CEST 2011

On Wed, Aug 24, 2011 at 02:37:33PM +0200, Carl Eugen Hoyos wrote:
> 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

iam fine with adding the lists but iam not mkv maintainer (in cc)


Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Democracy is the form of government in which you can choose your dictator
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