[Mp4-tech] [Video] two questions on H.264 HRD
Gary Sullivan
garysull windows.microsoft.com
Tue Jul 11 22:17:43 EDT 2006
I believe the answer is Yes.
Best Regards,
Gary
________________________________
From: Nancy Johnson [mailto:nancyjohnson111 yahoo.com]
Sent: Tuesday, July 11, 2023 12:40 PM
To: Gary Sullivan; mp4-tech lists.mpegif.org
Subject: RE: [Mp4-tech] [Video] two questions on H.264 HRD
Thank you so much for helping me clarify this fundamental issue.
Now I don't have any question on HRD. So it's time for me to ask the
similar question on DUT for output timing conformance:
Will the DUT be assumed to know all the scheduling info of HSS
just as the HRD? If yes, are these info sent to DUT by other means not
specified in the spec? if no, does it mean the DUT has to figure them
out by ways which are not specified in the spec?
Best Regards,
Nancy Johnson
Gary Sullivan <garysull windows.microsoft.com> wrote:
I believe the answer is Yes.
(And if the HSS is using an "interpolated" schedule, you
can also assume that the HRD "knows" what that schedule is as well.)
Best Regards,
Gary Sullivan
________________________________
From: Nancy Johnson
[mailto:nancyjohnson111 yahoo.com]
Sent: Monday, July 10, 2023 4:50 PM
To: Gary Sullivan; mp4-tech lists.mpegif.org
Subject: RE: [Mp4-tech] [Video] two questions on
H.264 HRD
Can I derive from "HSS and HRD are hypothetical"
that "HRD will use the same SchedSelIdx value as that used by HSS (let's
temporarily exclude the case that HSS uses an "interpolated" delivery
schedule mentioned in spec p271 to simplify my question)? If no, how
should the HRD determine SchedSelIdx value it should use for
initial_cpb_removal_delay? If this is out of the scope of the spec, I
don't think the behavior of HRD is fully specified.
Sorry for still bothering you for this question.
Thanks a lot.
Best Regards,
Nancy Johnson
Gary Sullivan <garysull windows.microsoft.com>
wrote:
I suppose that the issue of needing to
feed the bitstream to the decoder in some fashion (including selecting
the SchedSelIdx or interpolated schedule and getting the data into the
decoder according to that schedule somehow) is the reason for the
concept of the HSS. Although the details of how to do that are out of
scope, I think the standard is pretty clear on what to do. The "H" in
HSS and HRD, of course, stands for hypothetical, which is an important
thing to keep in mind.
Best Regards,
Gary Sullivan
________________________________
From: Nancy Johnson
[mailto:nancyjohnson111 yahoo.com]
Sent: Friday, July 07, 2023 6:13 PM
To: Gary Sullivan;
mp4-tech lists.mpegif.org
Subject: RE: [Mp4-tech] two questions on
H.264 HRD
Dr. Sullivan,
Thanks for providing these valuable
information. Regarding to the value of SchedSelIdx,
1. I believe the HRD is a golden model
which will be used to test the conformance of bitstreams and real
decoders.
2. I believe the behavior of the HRD
have been accurately specified in the spec due to 1. However, if I were
asked to write a behavior model of the HRD by C or Verilog using the
spec, I don't know how the HRD can determine the value of
initial_cpb_removal_delay[SchedSelIdx] (at least it will influence the
coded picture removal time from the CPB and further influence the
decoded picture output time) because I can not find any information in
the spec for the HRD to know the value of SchedSelIdx it should use.
Maybe the HRD can derive an interpolated
initial_cpb_removal_delay according to the actual bit rate it detected.
Maybe the HRD is assumed to know an exact or interpolated value of
SchedSelIdx from some system level info outside the bitstream. But this
is not mentioned in the spec.
I wish my question was invalid just
because I misunderstood something or missed something.
Thanks a lot.
Best Regards,
Nancy Johnson
Gary Sullivan
<garysull windows.microsoft.com> wrote:
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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