title: AVPlayer with one video tracks and multiples audio tracks
body: <p>I'm trying to make a player in my App capable to have one video tracks and multiples audio tracks (for differents languages).</p>
  
  <p>I've done this but the player won't launch : </p>
  
  <pre><code>AVMutableComposition *composition = [AVMutableComposition composition];
  AVURLAsset* videoAsset = [[AVURLAsset alloc]initWithURL:urlVideo options:nil];
  
  AVMutableCompositionTrack *compositionVideoTrack = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
  NSError* error = NULL;
  
  [compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero,videoAsset.duration) 
                                 ofTrack:[[videoAsset tracksWithMediaType:AVMediaTypeVideo]objectAtIndex:0] 
                                  atTime:kCMTimeZero
                                   error:&amp;error];
  
  NSMutableArray *allAudio = [[NSMutableArray alloc]init];
  for (int i=1; i &lt; [allAudioTracks count]; i++) {
      NSURL *audioURL = [NSURL URLWithString:[NSString stringWithFormat:@"%@%@",URL_MEDIA,[[allAudioTracks objectAtIndex:i]audio]]];
      AVURLAsset* audioAsset = [[AVURLAsset alloc]initWithURL:audioURL options:nil];
      [allAudio addObject:audioAsset];
      [audioAsset release];
      [audioURL release];
  }
  
  for (int i=0; i &lt; [allAudio count]; i++) {
      NSError* error = NULL;
      AVURLAsset *audioAsset = (AVURLAsset*)[allAudio objectAtIndex:i];
      //audioAsset = [allAudio objectAtIndex:i];
  
      AVMutableCompositionTrack *compositionAudioTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
      [compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero,audioAsset.duration) 
                                      ofTrack:[[audioAsset tracksWithMediaType:AVMediaTypeAudio]objectAtIndex:0]
                                       atTime:kCMTimeZero
                                        error:&amp;error];
  
      NSLog(@"Error : %@", error);
      //[allCompositionTrack addObject:compositionAudioTrack];
      [audioAsset release];
  }
  </code></pre>
  
  <p>and I try to start my player like this :</p>
  
  <pre><code>AVPlayerItem *playerItem = [[AVPlayerItem alloc]initWithAsset:composition];
  
  player = [[AVPlayer alloc]initWithPlayerItem:playerItem];
  
  layerVideo = [AVPlayerLayer playerLayerWithPlayer:player];
  layerVideo.frame = CGRectMake(0, 0, 480, 320);
  [self.view.layer addSublayer:layerVideo];
  
  [player play];
  </code></pre>
  
  <p>But nothing append.
  Thanks for your help (and sorry for my English :))</p>