Reduce framerate before downscaling #7022
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It is cheaper to drop frames and downscale those that remain than it is to downscale all frames and then drop some of them. This is achieved with the filter chain `-cv fps=FPS,scale=W:H`, and perhaps was the original intention. The plain `-r` and `-s` flags do not execute in order though - they each put themselves at the *end* of the filterchain, so `-r FPS -s WxH` actually applies the scale filter first, and then the rate filter. This fix can halve the CPU used by the detect ffmpeg process.
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We had problems with this approach in the betas, using |
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The relevant PR is #5210 |
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@NickM-27 Do you remember the specifics? You'd set it to 5 fps and sometimes get 5.1? Can I replicate? If it's not worth the effort...I brought back the |
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No, it was multiple frames off on my cameras. Usually would be 6 or 7 even though it was set to 5 |
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I have never been able to get ffmpeg to be consistent with fps dropping and smooth video across different cameras unless I re-encode the video after scaling and dropping using nvidia gpus. I’ve never tried cpu but nvidias cards drop frames or generate corrupt ones which they claim the -vsync 0 is needed to prevent. I thought there had to be a better way but I just gave up doing it in Frigate and do a full duplicate and transcode outside of frigate using another application. |
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@NickM-27 ICYMI, I brought back the |
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Makes sense, how much performance improvement are you seeing in this case? |
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With HW decoding but SW scaling, this reduces ffmpeg CPU load from 58% to 33% (on my Xavier with a single camera stream) |
It is cheaper to drop frames and downscale those that remain than it is to downscale all frames and then drop some of them. This is achieved with the filter chain
-cv fps=FPS,scale=W:H, and perhaps was the original intention here. The plain-rand-sflags do not execute in order though - they each put themselves at the end of the filterchain, so-r FPS -s WxHactually applies the scale filter first, and then the rate filter.This fix can halve the CPU used by the detect ffmpeg process.