Exposing Subtitles

The PSDK notifies the player client about the availability of internal AVAsset’s availableMediaCharacteristicsWithMediaSelectionOptions through the PTMediaPlayerMediaSelectionOptionsAvailableNotification notification. The available subtitles can then be accessed through the PTMediaPlayerItem property, subtitlesOptions.

To expose subtitles:

The client registers itself as a listener for the PTMediaPlayerMediaSelectionOptionsAvailableNotification notification:

[[NSNotificationCenter defaultCenter] 
  addObserver:self selector:@selector(onMediaPlayerItemMediaSelectionOptionsAvailable:) 
  name:PTMediaPlayerMediaSelectionOptionsAvailableNotification object:self.player];

When the client receives this notification, it implies that PTMediaPlayerItem has the available subtitles ready. The onMediaPlayerItemMediaSelectionOptionsAvailable method needs to be similar to this:
```
- (void) onMediaPlayerItemMediaSelectionOptionsAvailable:(NSNotification *) notification {
    NSArray* subtitlesOptions = self.player.currentItem.subtitlesOptions;
    NSArray* audioOptions = self.player.currentItem.audioOptions;
}
```
See "Implementing Alternate Audio" for information about alternate audio tracks.