__weak typeof(self) weakSelf = self;
/* Update the scrubber during normal playback. */
[weakSelf.player addPeriodicTimeObserverForInterval:CMTimeMakeWithSeconds(interval, NSEC_PER_SEC)
queue:NULL /* If you pass NULL, the main queue is used. */
usingBlock:^(CMTime time)
{
[self syncScrubber];
}];