[FFmpeg-user] Disparity in VMAF scores

Kamaldeep Tumkur kamaldeep.tumkur at gmail.com
Sun May 8 13:07:08 EEST 2022


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:


external encode:


Thank you.

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