A few commits ago, the render behavior was changed to only render within a
user-specified range of the playhead. This works well, but it would still
render from the start of the range (usually before the playhead) to the end,
meaning it couldn't keep up with the playhead as well as it should. This
commit prioritizes frames close to the playhead and renders outwards to
address this.
This index system will have awareness of the disk cache state and be able to
fill in and store frames as necessary while keeping the disk cache under
user defined limits.
itsmattkc