Hello,
I am downscaling some 4K videos to 1080p with FFmpeg.
Both input and output should be standard H.264 - 8-bit, YUV 4:2:0.
I'm not quite sure if I understand the meaning of the following scaler flags - could you help me with these?Thanks!
- full_chroma_inp - this forces scaler to treat the input as full YUV 4:4:4, right? So it doesn't make sense to use it in my case?
- full_chroma_int - this is about using the full YUV 4:4:4 for internal processing when rescaling? Would it change anything if I apply -pix_fmt yuv420p afterwards anyway?
- accurate_rnd - "Enable accurate rounding". I assume it is somewhat slower but more precise mode? Which would result in a slightly sharper result?
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Did that.
In my case - when both input and output are yuv420p - the following settings produce binary-identical output files:
Code:-sws_flags spline+accurate_rnd+full_chroma_int+full_chroma_inp -pix_fmt yuv420p -sws_flags spline+accurate_rnd+full_chroma_int -pix_fmt yuv420p -sws_flags spline+accurate_rnd -pix_fmt yuv420p
Last edited by pachura; 19th Jun 2018 at 01:37.
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Well... knowing ffmpeg a bit i can say only one thing - perhaps they fixed some issues and some behaviour before non-default is now default but my observations on ffmpeg way before rev 3 leaded me to conclusion to use those flag as integral part of any resize on ffmpeg.
And one question - are you observing speed difference for those flags? If not then it may explain lack of difference between tries - perhaps they are active by default (so you could replace + sign with - sign and check how ffmpeg behave with explicitly disabled flags).
I will be not surprised if those flags are now active by default.
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