[FFmpeg-user] Unable to accurately split vmaf calculation

[Ferdi Scholten]

Hi,
> I am trying to split vmaf calculation work across multiple threads by
> logically dividing the video ( not literally )
>
> I tried following 2 commands to do vmaf on a 20.08 sec ( 477 frames ) video
>
> *For 1st 10 second: *
>
> *ffmpeg -i transcodedA.mp4 -i sourceA.mxf -filter_complex
> "[0:v][1:v]scale2ref=flags=bicubic[encoded][source];[source]format=pix_fmts=yuv420p,trim=start=0,trim=end=10,setpts=PTS-STARTPTS[source2];[encoded]trim=start=0,trim=end=10,setpts=PTS-STARTPTS[encoded1];[encoded1][source2]libvmaf=feature='name=psnr|name=float_ssim|name=float_ms_ssim':n_threads=4:log_fmt=json:log_path=A0-10.json"
> -f null -*
>
>
> *For remaining part of video:*
>
> *ffmpeg -i transcodedA.mp4 -i sourceA.mxf -filter_complex
> "[0:v][1:v]scale2ref=flags=bicubic[encoded][source];[source]format=pix_fmts=yuv420p,trim=start=10,setpts=PTS-STARTPTS[source2];[encoded]trim=start=10,setpts=PTS-STARTPTS[encoded1];[encoded1][source2]libvmaf=feature='name=psnr|name=float_ssim|name=float_ms_ssim':n_threads=4:log_fmt=json:log_path=A10-20.json"
> -f null -*
>
> But in both output files, collectively I get only 465 frames, that means 13
> frames missing. What can I do that ensure no frame is missed?
>
>
>
> Regards,
> Tarun Singhal
> _______________________________________________
>
Most likely the split is not at a keyframe.
This does not matter for the first part, but it does for the second 
part, that has to start on a keyframe. You will be missing all the 
frames from the 10s where the first vide ends, to the first keyframe 
after the 10 seconds which is where the second video starts.
So only split at keyframes, or just process the entire file without 
spitting (will be more accurate too)