[Mp4-tech] H.264 DPB storage

[EricChuang via.com.tw]

Hi Gary,
Thanks for your answering on question 1.
Regarding Question 2, maybe I did not describe it clear. My question is
the DPB operation described in Annex C is to store both reference and
non-reference pictures. But the DPB size is limited. When DPB is full,
and at the time it contains both reference and non-reference pictures,
one of the non-reference picture would be picked up first, and output
forcely to get a space for storing the incoming reference picture. 
And if I implement DPB to store reference pictures only, and manage
pictures for output in another way without occupying DPB slots, the DPB
slots would be totally used for storing reference pictures, and there
might be less chance to force non-reference picture output.
These 2 methods would have the same output order, but the output timing
might not be the same. In Annex C.4, it reads two conformance types can
be claimed by decoder, one of them is output timing conformance, and the
other is output order conformance. My question is the implementation not
storing non-reference pictures in DPB break the output timing
conformance ?
Thanks,
Eric
-----Original Message-----
From: Gary Sullivan [mailto:garysull windows.microsoft.com] 
Sent: Monday, February 20, 2024 9:58 AM
To: Eric Chuang; mp4-tech lists.mpegif.org
Subject: RE: [Mp4-tech] H.264 DPB storage
Eric,
Regarding your Question 1, when referring to a bitstream, Annex A
specifies the constraints that must be obeyed by the bitstream; when
referring to a decoder, it specifies the class of bitstreams that the
decoder must be able to handle.
Regarding your Question 2: Your question is somewhat hard to understand.
The basic question seems to have something to do with whether the
confromance requirements are different depending on whether particular
pictures are reference pictures or not.  There is no such distinction
drawn in the standard.  The conformance requirements apply to all
pictures.  Clearly, if some pictures are not decoded properly, the
functional degradation experienced in an application may be less severe
if the pictures that are messed up by a decoder are not reference
pictures (or are higher-level dependent sub-sequences).  However, that
kind of thing is not part of the specification of conformance in the
standard.
Best Regards,
Gary Sullivan
  _____  
	From: mp4-tech-bounces lists.mpegif.org
[mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of
EricChuang via.com.tw
	Sent: Sunday, February 19, 2024 7:06 PM
	To: mp4-tech lists.mpegif.org
	Subject: [Mp4-tech] H.264 DPB storage
	Hi Experts,
	I have two questions regarding the DPB storage.
	1. The standard specifiy the method to decide the maximum DPB
slot count in Annex A, depending on the level value. Does this level
means decoder level or bitstream level ?
	2. In Annex C, the DPB operation described is used for both
reference picture and non-reference picture, is this an enforcement ? If
I let DPB storing reference picture only, and create another mechanism
for managing non-reference picture, and handle the reoder and
no_output_of_prior_pics_flag, would this cause any decoder conformance
problem ?
	Thanks very much for your answering in advance,
	Eric
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