Some files may provide different caps insight of one stream. Since
vp9enc support caps reinit, we should support cache reinit too.
If more then file cache file will be created, the naming will be:
cache cache.1 cache.2 ...
Based on patch by: Oleksij Rempel <linux@rempel-privat.de>
https://bugzilla.gnome.org/show_bug.cgi?id=747728
... instead of just counting frames. The values are supposed to be in timebase
units, not frame units. This fixes various quality problems with VP8/VP9
encoding and in general makes the encoder behave better.
Thanks to Nirbheek Chauhan for noticing this bug.
