[FFmpeg-devel] [PATCH] gifdec: resync support

[Don Moir]

> also, i would prefer that seek index is built and real seek support is
> added eventually.

For me I needed the duration as well. I started out by making this optional but I did not like that and decided to compute the 
duration internally for the time being. But by computing the duration, you then know additional possible keyframes and the total 
number of frames. In practice it's quick but I suppose there could be times when scanning the file could be time consuming.