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So I have a raw video in yuv420p format - input.yuv, and I know its frame size. I execute 2 commands:

ffmpeg -pix_fmt yuv420p -s 352x288 -i input.yuv -pix_fmt yuv422p input_yuv422p.yuv

and then

ffmpeg -pix_fmt yuv422p -s 352x288 -i input_yuv422p.yuv -pix_fmt yuv420p input_decoded.yuv

The problem is that files input.yuv and input_decoded.yuv differ. My understanding is that when we convert to yuv422p from yuv420p - we should essentially copy existing U and V components to produce more samples to fill in; then, when converting back - we should simply drop these samples, and receive the original file back, but that's not what I see. Am I doing something wrong here, and is it possible to receive original yuv420p back?

IvanIvanovich
  • 31

1 Answers1

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It seems that ffmpeg performs some interpolation when upsampling from 420 to 422 and antialiasing when downsampling back from 422 to 420 - at least that's the default behavior of similar Matlab library: mathworks.com/help/vision/ref/chromaresampling.html. And it looks like this library actually has the options to achieve the behavior of simply copying/dropping chrominance values which would result in no difference between the original yuv420p and "converted back", in case anyone also needs this.

IvanIvanovich
  • 31