[FFmpeg-user] Disparity in VMAF scores

[Kamaldeep Tumkur]

So my question is, does libvmaf implementation do any kind of detection of
audio in the distorted asset before computing a perceptual video quality
score.


On Mon, 9 May 2022 at 13:37, Kamaldeep Tumkur <kamaldeep.tumkur at gmail.com>
wrote:

> @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.
>>
>