Recommended options for best quality in real-time mode (VP9)

[djco...@gmail.com]

Hello,

I've been tinkering with different values for --cpu-used in real-time mode to reach a particular encoding speed --

now I'm trying to figure out what combination of options would generate the best possible quality video.

In specific, I'm working with a YUV file, encoding it to 2000 kb/s CBR with --cpu-used=6. Here is what

my command line looks like, presently:

vpxenc --codec=vp9 --width=${width} --height=${height} --fps=${fps} --end-usage=cbr
       --target-bitrate=2000 --rt --cpu-used=6 -o ${output}.webm ${input}.yuv

I know that many of the options are situational and real-time mode encoding speed/quality is dependent upon the 

specifications of the machine being used, but in general, what settings would you recommend to increase 

quality (for example, in terms of PSNR) given these constraints? I tried --undershoot-pct=1 on a whim and 

while PSNR did increase, the resulting bitrate was much higher than 2000 kb/s. Anyway, any suggestions

would be greatly appreciated.

Thanks,

Dennis

[Yunqing Wang]

Hi Dennis,

For 1-pass real-time encoding, you can limit the quantizer to improve the quality, such as: --min-q=2 --max-q=56, and also try the AQ mode: --aq-mode=3

Yunqing

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[djco...@gmail.com]

Hi Yunqing,

The settings you recommended did improve quality for the most part. I noticed, however, that with certain videos ("busy" ones, with a lot of action), the output bitrate was much higher than the specified target (i.e. for a target bitrate of 500 kb/s, the output was 2577 kb/s). Why does this happen?

Thanks,

Dennis 

[Yunqing Wang]

If you need to limit the bitrate undershooting/overshooting, use these options:  --undershoot-pct=50 --overshoot-pct=50. Adjust the values to achieve your goal. There is always a trade-off between quality and bitrate.

Yunqing