title: How do you disable all text tracks in an AVMutableComposition?
body: <p>Let's say I have an AVMutableComposition with 4 tracks: 1 video, 1 audio, and 2 text tracks. I can switch between the two text tracks by toggling the enabled flag like so:
  <code>
  [_player.currentItem.tracks[2] setEnabled:NO];
  [_player.currentItem.tracks[3] setEnabled:YES];
  </code></p>
  
  <p>However if I attempt to turn off captions by setting enabled NO on both tracks, the most recent text track will get stuck on the screen. Is there a way to disable all text tracks?</p>