[Mp4-tech] two questions on H.264 HRD

[Gary Sullivan]

Regarding question 1 -- I think you would need to read the HD DVD specs
to find out, but personally I would not recommend trying to sell a lot
of units of an HD DVD player that can't be output timing conforming at
least the vast majority of the time for the vast majority of movie
content.
Regarding question 2 -- It is important to distinguish between the
operation of a real decoder in a real system environment and decoder or
bitstream unit testing for conformance.  For output timing conformance
testing purposes, we assume that the HSS can force-feed the decoder in a
manner consistent with the standard somehow, but we really don't care
how.  It doesn't have to exclusively consist of the use of information
within the bitstream.  Also note that HRD decoder testing is not
necessarily performed by just selecting a value of SchedSelIdx -- there
is also the possibility of "interpolated" scheduling.  There are really
two different kinds of constraints specified in the standard -- checks
that a conforming bitstream must be able to fulfill and checks that a
conforming decoder must be able to fulfill.  It's important not to
confuse the two.  Also, when operating in a real system environment, the
system will ordinarily have some additional way of conveying the
bitstream and associated timing information to the decoder.  In the case
of HD DVD there are a significant amount of timing issues that are
controlled at the MPEG-2 systems level rather than needing to rely on
the information within the video elementary bitstream and I believe the
system-level information and operation should ordinarily be considered
more important to the actual operation of a real decoder in such an
application environment.
Best Regards,
Gary Sullivan
________________________________
	From: mp4-tech-bounces lists.mpegif.org
[mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of Nancy Johnson
	Sent: Thursday, July 06, 2023 4:38 PM
	To: mp4-tech lists.mpegif.org
	Subject: [Mp4-tech] two questions on H.264 HRD
	Dear H.264 experts,
	Could you please help me to figure out these 2 questions?
	1. For HD-DVD decoding application, is it necessary for the
H.264 decoder to claim output timing decoder conformance? It seems that
for this case the decoder can be fed the bit stream in an "on demand"
way.
	2. According to page 267 equation C-7 of H.264 03/2005, the
removal time of the access unit from the CPB will be influenced by
initial_cpb_removal_delay[SchedSelIdx]. Although
initial_cpb_removal_delay[i] (i=0~cpb_cnt_minus1) are sent to HRD by
buffering period SEI message (page 277 section D.1.1 of H.264 03/2005),
I can not find a way in the H.264 stream definition for the HRD to know
the specific value of SchedSelIdx in equation C-7. If this is true, how
to make sure the value of SchedSelIdx in equation C-7 used by DUT are
the same as that used by HRD? (Is this necessary for the decoder to meet
output timing conformance?)
	Thanks a lot.
	Sincerely yours,
	Nancy Johnson
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