Filip Roséen authored May 21, 2016 and Jean-Baptiste Kempf committed May 23, 2016

There is sadly a trade-off between having "perfect" seeking for all
tracks (ie. the preroll should start at the latest possible location for
all tracks within the mkv), and having seeking which is fast.

This patch changes the functionality in SegmentSeeker so that it
optimizes seeking for the most important tracks. If, during the scan for
seekpoints for these tracks, we stumble upon seekpoints for other tracks
- use them, if not; simply yield appropriate seekpoints for the priority
tracks.

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>