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

[Isaac Sutherland]

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.

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?

Isaac