[Ffmpeg-devel] ISO MPEG4 VO header description?

Bill May wmay
Wed Feb 8 21:59:47 CET 2006

Patrice Roulet wrote:
> Hi
> 	I would like to know if anybody could explain me the VO header in ISO MPEG
> 4.
> 	I receive a MPEG 4 streamming frames and I need to generate VO header to
> put it in AVCodecContext::extradata
> 	I have only the width and height.
> 	Which values should I set to profile, frameRate, shortTime, variableRate
> and quantType.

Mpeg4 has several headers that give information about the encoding
used in the stream.

The VO, VOL, VOSH all have information that can be used; the VOL is the
key piece to the puzzle.

These are described in ISO/IEC14496-2, section 6.2.3 (Video Object layer).

If you're streaming using RTP, these fields (as hex digits) should be located
in the SDP in the a=fmtp statement, config= heading.  For RFC3016, those
fields are not included in the stream.

If you're doing something else, you'll have to parse for those; for decoding
with ffmpeg, you should pass them first to the decode, and will be the
generated in the first encoded frame.


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