[Mp4-tech] H.264 frame rate

[ChenJianjun]

Thanks,Gary!
The reason I cared about "frame rate" is I am wondering how does decoder know when to output a picture. So it seems that there are three places that can decide when to output a picture:
1) system-level or application-level that you mentioned,it should be a constant frame rate.
2) VUI parameter,it will point out frame rate is fixed or non-fixed, and the frame rate value if it is fixed.
3) Picture timing SEI message semantics(SPEC D.2.2), it can calculate a clocktimestamp for each picture, but the parameter"time_scale" and "num_units_in_tick" derives from 2).
So my new question is what's the relationship between 1),2) and 3)? Can I conclude as follows:
if 1) exists, 2)and 3) does not exist;
if 1) does not exist, and if 2) point out a fixed frame rate, then 3) does not eixt;
if 1) does not exist, and if 2) point out a non-fixed frame rate, then 3) exists.
Thanks!
Subject: RE: [Mp4-tech] H.264 frame rateDate: Tue, 14 Aug 2023 10:58:22 -0700From: garysull windows.microsoft.comTo: cjj730 hotmail.com; mp4-tech lists.mpegif.org
Please define the term frame rate.  Are you under the impression that the number of decoded pictures per second needs to be a constant?  If so, that is an incorrect impression in some use cases.
If there is no frame rate expressed in the video elementary stream syntax, there may be such an animal defined in a system-level or application-level specification.
If there isn't, then it is possible that the video bitstream does not have a frame rate (depending on your definition of what a frame rate is).
However, there will be a constraint on how close together in time the decoder can be required to decode each pair of consecutive pictures in the bitstream in decoding order.  Similarly there will be a constraint on how close together in time the decoder can be required to output each pair of consecutive pictures in the bitstream in output order.  Those constraints are specified by the level constraints in Annex A.
Best Regards,
Gary Sullivan
From: mp4-tech-bounces lists.mpegif.org [mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of ChenJianjunSent: Tuesday, August 14, 2023 5:41 AMTo: mp4-tech lists.mpegif.orgSubject: [Mp4-tech] H.264 frame rate
Dear experts: How to calculate the H.264 frame rate? I noted that VUI parameter(SPEC E.1) and Picture timing SEI message semantics(SPEC D.2.2) may have such information.But they are optional,then how to get the frame rate information if there's no such information? Thanks!
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