[Mp4-tech] [H.264] Use of SPS/PPS in H.264

[Dave Singer]

Don't forget that although the AVC core specification doesn't place 
limits on the number of SPS/PPS, how often they change etc., it's 
perfectly legitimate for an environment that *uses* AVC to limit
* profiles
* levels
* changes in visual size
* pixel aspect ratios, color spaces, etc.
* numbers of SPS/PPS
* whether updates of SPS/PPS are out of band or in band in the video 
stream, if they are allowed
* whether 'Paris' appears in the video sequence
and so on.
At 9:58  +0000 22/06/06, arun menon wrote:
>Hi Erez,
>
>Please my comments below.
>
>Thanks,
>Arun
>
>
>On Wed, 21 Jun 2023 Steinberg Erez-RM96322 wrote :
>>Hi,
>>
>>H.264 allows up to 32 sequence parameter sets (SPS) and 256 picture
>>parameter sets (PPS) in a stream.
>>
>>An SPS includes information on the picture resolution, number of
>>reference frame, profile and level. These are cardinal for decoder
>>initialization and setup.
>>
>>My questions:
>>
>>(1) Is a decoder expected to handle spontaneous changes in these
>>parameters? I.e., if an IDR picture is received with a different
>>PPS/SPS, is it supposed to reallocate all its memory buffers? (This is
>>effectively resetting the decoder)
>---------------------------------------------------------------------
>An example I can think of when the decoder will receive SPS and PPS 
>information with different picture resolution could be during 
>playing of live content. If at any time the encoder finds that the 
>network bandwidth is reduced due to some reason, it could encode and 
>send smaller frame size. In this case you should reallocate the 
>memory buffers used for the frames. Alternatively you can allocate 
>your memory buffers with the max size supported to prevent the 
>freeing and reallocation.
>----------------------------------------------------------------------
>>
>>(2) For practical implementations -- are there any known applications
>>that use different SPSs in the same stream? Or, can a decoder assume
>>only one SPS?
>>
>   It would be wrong if the decoder assumes that there would be only 
>one SPS or PPS because you do get multiple SPS and PPS in some 
>streams. But there is also the possibility that sometimes the same 
>information in SPS and PPS is sent again, instead of some thing 
>different (I have encountered a few such clips).
>>
>>Thanks for your help!
>>
>>Regards,
>>Erez
>>
>>_______________________________________________
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>>
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>
>
>
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>_______________________________________________
>NOTE: Please use clear subject lines for your posts. Include [audio, 
>[video], [systems], [general] or another apppropriate identifier to 
>indicate the type of question you have.
>
>Note: Conduct on the mailing list is subject to the Antitrust 
>guidelines found at 
>http://www.mpegif.org/public/documents/vault/mp-out-30042-Antitrust.php

-- 
David Singer
Apple Computer/QuickTime
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