[Mp4-tech] H264 standard question

[Gary Sullivan]

Victor et al,
Your use of the word "picture" corresponds to what the standard calls an "access unit".  An "access unit" contains a number of NAL units, not the other way around.
However, to be precise, not all access units necessarily contain picture parameter sets.  A single picture parameter set may be used in the decoding process of multiple pictures (and a picture parameter set may hypothetically appear in the bitstream within an access unit that does not use that particular picture parameter set -- and picture parameter sets can also hypothetically be conveyed outside the elementary bitstream although I believe that is not common practice).  That is the basic distinction between a conventional "picture header" and a "picture parameter set".
You should not assume that sequence parameter sets and picture parameter sets are exactly the same thing as conventional sequence headers and picture headers.
Best Regards,
Gary Sullivan
________________________________
From: mp4-tech-bounces lists.mpegif.org [mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of Victor lyamtsev
Sent: Friday, October 19, 2023 11:04 AM
To: mp4-tech lists.mpegif.org
Subject: [Mp4-tech] H264 standard question
Hi,
Is all data in H264 stream sequenced inside NAL units?
E.g. does one NAL unit contain one or more pictures ?
Or, other way around, picture data contains picture parameter set and number of NAL units?
just trying make sure I read spec correctly...
Thanks,
-vl
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