Lower FPS and CPU utilization with VMAF v2.0.0 with FFmpeg

[LarLei]

Hello,

With ffmpeg-2020-12-12-git-5148740e79-full_build (https://www.gyan.dev/ffmpeg/builds/packages/ffmpeg-2020-12-12-git-5148740e79-full_build.7z) that has VMAF v2.0.0, the FPS is much lower (around 10) and the CPU utilization averages around 20%.

However, with ffmpeg-2020-11-18-git-e3081d6f4f-full_build (no longer available for download) that has VMAF v1.5.3, the FPS averages around 25 and the CPU utilization is at 100%.

The CPU is an Intel i7-9750H (6 cores, 12 threads, AVX2)

I use 1 below for FFmpeg with VMAF v1.5.3 and 2 below for FFmpeg with VMAF v2.0.0:

1. ffmpeg -report -benchmark -i Transcode.mp4 -i Source.mp4 -lavfi libvmaf=model_path=D\:/Software/FFMPEG/cmds/vmaf_v0.6.1.pkl:pool=harmonic_mean:log_fmt=xml:log_path=C\:/Save/%Transcode%.VMAF.xml -f null -

2. ffmpeg -report -benchmark -i Transcode.mp4 -i Source.mp4 -lavfi libvmaf=model_path=D\:/Software/FFMPEG/cmds/vmaf_v0.6.1.json:pool=harmonic_mean:log_fmt=xml:log_path=C\:/Save/%Transcode%.VMAF.xml -f null -

Thanks!

[malakudi]

Add n_threads=X to your libvmaf parameters where X the number of threads you want. It seems 2.0 uses only 1 thread when n_threads is not defined.

[kylophone]

Add n_threads=X to your libvmaf parameters where X the number of threads you want. It seems 2.0 uses only 1 thread when n_threads is not defined.

Yes, this is correct. Previous libvmaf would query your system and use all the available cores by default. The default in libvmaf v2.0.0 is to use no threading. Use n_threads to explicitly set the number of threads to be used.

[LarLei]

Thanks all! That fixed the issue. I modified the command 2 above to include the n_threads=12 and saw a nice improvement of 35 FPS with the CPU at 100% for all cores/threads.

ffmpeg -report -benchmark -i Transcode.mp4 -i Source.mp4 -lavfi libvmaf=model_path=D\:/Software/FFMPEG/cmds/vmaf_v0.6.1.json:pool=harmonic_mean:n_threads=12:log_fmt=xml:log_path=C\:/Save/%Transcode%.VMAF.xml -f null -