[FFmpeg-user] How to lossless crop mp4 videos

[Nicolas George]

Ulf Zibis (12021-08-16):
> if I understand correct, mp4 videos are encoded in blocks of 16x16
> pixels. I I'm wondering if I could crop a video by multiples of 16
> pixels without reencoding the remaining blocks.

It depends on the codec, not the format.

With a codec like MJPEG, it is possible. There are tools to do it with
individual images, look up jpegtran.

But with video codecs that use temporal compression, a visible part of
the next image can depend on a cropped part of the current image, and
that makes it impossible.

Regards,

-- 
  Nicolas George
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