[Mp4-tech] [Video] question on level_prefix of H.264
Nancy Johnson
nancyjohnson111 yahoo.com
Fri Oct 13 21:45:15 ESTEDT 2006
Dear Experts,
On page 249 and 250 of ITU-T Rec. H.264 (03/2005), the value of level_prefix is limited to not greater than 15 for base/main/extended profiles. But there is no such limit for high profile. Without this, how to control the size of level_prefix and level[i] for CAVLC in the hardware? Note that level[i] is related to levelCode, which is related to ((1<<(level_prefix-3))-4096)? Thanks.
Rgs,
Nancy
Nancy Johnson <nancyjohnson111 yahoo.com> wrote:
Thanks a lot, Dr. Sullivan. That's all my question on H.264 currently and I have got all the answers from you.
Best Regards,
Nancy Johnson
Gary Sullivan <garysull windows.microsoft.com> wrote:
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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