[FFmpeg-devel] Handling MPEG-4 Custom User Data

Michael Niedermayer michaelni
Tue Aug 18 23:03:11 CEST 2009

On Tue, Aug 18, 2009 at 04:35:04PM -0400, Isaac Sutherland wrote:
> MPEG-4 allows a video producer to embed custom data in GOV headers. It is my
> understanding that the MPEG standard requires video applications to preserve
> such custom user data (e.g. when transcoding between MPEG formats)
> regardless of whether they understand what it's supposed to be used for. At
> least, that's the impression I get from
> http://en.wikipedia.org/wiki/MPEG_user_data.

wikipedia is of no relevance, its a world writeable reference not primary
litrature, quote the ISO spec please

> However, ffmpeg doesn't appear to allow applications to consume this data,
> or at least I can't see how it does. decode_user_data in libavcodec/h263.c
> appears to check for a few data strings (xvid, divx, and ffmpeg identifiers)
> but throws away unrecognized data. Is providing support for passing custom
> user data to the user within the scope of ffmpeg? If so, any suggestions on
> how this should be implemented?

its sure fine to export user data from the decoder to the user app through
a AVCodecContext.user_data if someone submits a clean patch.
Though i am not sure how usefull such a feature would be ...

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Asymptotically faster algorithms should always be preferred if you have
asymptotical amounts of data
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