Fix unused imports, double null checks and synchronization
Flowplayer does not support WTT subs properly so use hardcoded FFmpeg
subs
Revert "Flowplayer does not support WTT subs properly so use hardcoded FFmpeg subs"

This reverts commit dc401535eecf1e6dd98e7d27822291ec04f0aeec.
Do not hardcode subs for WebPlayer