[theora] Keyframes

Gregory Maxwell gmaxwell at gmail.com
Mon Aug 24 14:39:47 PDT 2009

On Mon, Aug 24, 2009 at 5:35 PM, mesecam<mesecam at gmail.com> wrote:
> Hi all,
> First of all a big thank you for your work.
> I would like to know what is (could be) the best (optimal in a psnr
> and/or subjectivity sense) maximum distance between keyframes
> or is theora using a good heuristic change scene detection mecanism?
> Does it really matter to theora as with mpeg4 part2/10?
> Thank you and keep up the good work

Theora will place keyframes where they make sense from a compression
efficiency perspective regardless of the requested maximum interval.
It should never degrade quality to increase the interval*.

The reason you shouldn't use enormous keyframe intervals is that it
makes it hard to seek and cut the resulting files.

If you do find any good test clips that perform clearly better with
shorter keyframe intervals I'm sure there are people who would love to
see them.

(*) However, in one pass mode the buffer size (buf-delay) is set to
the same size as the keyframe interval, so don't confuse the effect of
changing the buffer size with the effect of changing the keyframe

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