[FFmpeg-user] Disparity in VMAF scores

[Kamaldeep Tumkur]

@Clayton, thanks for your response.

It turned out that the external encoder was adding an audio track to the
encode. This was throwing the libvmaf scores off. On removing the audio
track and checking the encode, the score jumped from 25 to 77.64.

Now there is basis to compare the ffmpeg and the external encode.

Regards
Kamaldeep



On Sun, 8 May 2022 at 15:37, Kamaldeep Tumkur <kamaldeep.tumkur at gmail.com>
wrote:

> Hello,
>
> I'm new to the computation of VMAF scores using libvmaf in ffmpeg. While
> trying out generating scores through libvmaf, I have an issue that I cannot
> seem to find an explanation for.
>
> I encoded the 'crowd_run' HQ MP4 with two different encoders. The
> resulting files were compared with the same source (original).
>
> VMAF score of ffmpeg encoded clip:
>
> [libvmaf @ 0x7fc5d8f2cb00] VMAF score: 90.644028
>
>
> Command used:
>
> ffmpeg -i crowd_run_1080p50.mp4 -c:v libx264 -g 100 -keyint_min 100
> -sc_threshold 0 -b:v 12000k -maxrate 15000k -bufsize 15000k -c:a copy -f
> mpegts pass2.ts
>
>
> VMAF score for externally encoded clip:
>
> [libvmaf @ 0x7fc53d729500] VMAF score: 25.168431
>
>
>
> I just don't know how to explain this disparity in generated scores when
> framerates and resolution of the source were retained. The second clip
> doesn't seem to show such a degradation expected through the score.
> Attaching both the encoded clips here for analysis.
>
>
> Could anyone point me to why the external encoder generates an output with
> low VMAF score. Anything in the frame structure?
>
>
> ffmpeg encode:
>
>
> https://drive.google.com/file/d/15-9YyNhYWJoTMxdmESkc7b0mPKKUMqG7/view?usp=sharing
>
>
> external encode:
>
>
> https://drive.google.com/file/d/1Mt2jP51KZ4vTG7SYPnJkCG1uMWqOadid/view?usp=sharing
>
>
>
> Thank you.
>