[Mp4-tech] RE: [jvt-experts] h264 : MaxBR and MaxCBP

[Gary Sullivan]

Satendra et al,
Ultimately you will need to refer to the equations that use these variables in subclause A.3.  There is no averaging involved.
Ordinarily, the encoder will use the MaxCBP buffering capacity to smooth out the fluctuations of the number of bits needed to represent the individual pictures with adequate fidelity, and the overall fidelity is basically governed by the overall BitRate capability of the channel or the Level (whichever is lower).
In scenarios where end-to-end latency is especially important (i.e. real-time communication), the latency can also be reduced by reducing the amount of the buffering capacity that is actually used by the bitstream (at the expense of decreased overall quality and increased fluctuation of quality).
The encoding processes for the selection of prediction modes, motion vectors, coded block patterns, quantization step sizes, quantization dead-zone ratios and such are the "knobs" that are used to control the fidelity and bit rate.
Best Regards,
Gary Sullivan
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From: jvt-experts-bounces lists.rwth-aachen.de [mailto:jvt-experts-bounces lists.rwth-aachen.de] On Behalf Of Satendra
Sent: Monday, March 03, 2024 6:58 AM
To: jvt-experts lists.rwth-aachen.de; mp4-tech
Subject: [jvt-experts] h264 : MaxBR and MaxCBP
Hi all,
what are the exact meaning of MaxBR and MaxCBP and how these two parameters are inter-related.
I am having some understanding, but still there are few questions.
Here's my understanding:
MaxCBP is the max buffer size needed for input encoded stream.
and MaxBR is the maximum bitrate for the stream.
My question is how MaxBR in Kbps is governing the encoded stream.
Over what duration does stream has to be bounded by this MaxBR.
1) averaged over full encoded stream, or
2) averaged over GOP, or
3) averaged over a second, or
4) averaged over a frame
Also, is it a Max bound or Average bound?
Suppose, If it is a average bitrate over a GOP, then dividing this among frames, intra frames will have higher bitrate to maintain same quality.
Or, if it is a frame level bound, then to preserve same quality among all frames, we will never use the full range, as Intra frames will determine the max bitrate.
I will be thankful, if someone can explain these parameters.
Best Regards
Satendra
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"We all agree on the necessity of compromise. We just can't agree on when it's necessary to compromise."  ------Larry Wall
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