[theora] variable frame rate

[ogg.k.ogg.k at googlemail.com]

> How well dose theora handle varaiable frame rate?
>
> I looking a using a rolling frame rate that move up and down
>
> from 1 frame per 60 second (no montion)
> to 100 frames per second (very fast montion eg: lightning)

You'll have a granule rate of 100.
At times when there's high motion, all frames emitted.
At times where you want a lower framerate, you emit dup frames for
those frames you wish to skip, still at 100 fps. These are 0 byte
packets, so quite cheap.

Some players are (were ?) known to be broken for those, though, you'll want to
check your favored player works with dup frames. If not, you can emit
actual frames which will end up saying "no change over the whole
frame", but they're something like 9 bytes IIRC, so that can add up.

I think ffmpeg2theora will automatically use those dup frames where
appropriate. If you want to control framerate manually though, you'll
have to do it yourself I think.