About the VBR algorithm

[Dillon14281118]

What't the theory of the VBR in Svt-HEVC? Are there some papers to introduce the VBR algorithm?
In Svt-HEVC,which functions implement vbr?

[tianjunwork]

Could you take a look at SVT-AV1 design doc? Both encoders share the same VBR algorithm.
Below are processes related to BRC.
Initial rate control process:
https://github.com/OpenVisualCloud/SVT-AV1/blob/master/Docs/svt-av1-encoder-design.md#initial-rate-control-process
Rate control process:
https://github.com/OpenVisualCloud/SVT-AV1/blob/master/Docs/svt-av1-encoder-design.md#rate-control-process
Let me know if you need further information.

[Dillon14281118]

Thank you,it's helpful.
When I use Svt-HEVC to encode a 1920x1080 seqs,I set
FrameRate=15,
RateControlMode=1
TargetBitRate=2048000 in Sample.cfg,
I use ffmpeg to calc the PSNR,the PSNR is always a little low. And the actual bitrate is a little high.
I want to know why? Is the vbr question?

[Dillon14281118]

And I run the same command in VBR mode several times,the result is a little different every time.

[tianjunwork]

https://github.com/OpenVisualCloud/SVT-HEVC#demo-features-and-limitations
When set to encode in VBR mode, the encoder does not produce a bit-exact output from one run to another

You can experiment with -encMode, which provide you different trade-off between speed and coding efficiency. With lower encMode, you should get higher PSNR.

[Dillon14281118]

Is vbr implemented in EbInitialRateControlProcess.c,EbInitialRateControlReorderQueue.c,EbInitialRateControlResults.c?
I want to learn more about vbr.

[tianjunwork]

Yes, BRC algo is mainly in EbInitialRateControlProcess.c and EbRateControlProcess.c.
Recommend you read high level encoder arch first, to understand the data and control flow.
https://github.com/OpenVisualCloud/SVT-AV1/blob/master/Docs/svt-av1-encoder-design.md#high-level-encoder-architecture
https://github.com/OpenVisualCloud/SVT-AV1/blob/master/Docs/svt-av1-encoder-design.md#inter-process-data-and-control-management

[Dillon14281118]

Have you compared svt-hevc with other open source codecs like x265,HM?