[PD] HD 1920 X 1080

Charles Goyard cg at fsck.fr
Fri Mar 14 10:51:46 CET 2014

Alexandros Drymonitis wrote:
> If you are aiming to JUMP to specific frames in
> > the video or play it backwards you would choose a different codec
> > than if you just want to play it from the beginning to the end
> > linearly.
> Could you give some examples? I don't know anything about this but would
> really like to. Could you explain why is it like this?

This is because with some codecs, to save storage space/bandwidth,
movies are made of a few full images (key frames), and partial images
that hold only the difference with respect to the previous keyframe. Say
there is 1 full frame for 24 partial frame.

So if you jump to a partial frame, the computer has to seek to a
keyframe and then to the diff frame, and rebuild the complete image from

mjpeg is just more or less a series of JPEG images in a queue. So when
you seek to frame x, there is less work to do. The downside is that
files are very large.

If you just read a movie linearly, you're good with keyframes and so.
If you want to jump all over the file like crazy, it could be more
efficient with mjpeg.

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