AVPlayer with one video tracks and multiples audio tracks

I'm trying to make a player in my App capable to have one video tracks and multiples audio tracks (for differents languages).

I've done this but the player won't launch :

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:&error];

NSMutableArray *allAudio = [[NSMutableArray alloc]init];
for (int i=1; i < [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 < [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]
                     开发者_JAVA技巧                atTime:kCMTimeZero
                                      error:&error];

    NSLog(@"Error : %@", error);
    //[allCompositionTrack addObject:compositionAudioTrack];
    [audioAsset release];
}

and I try to start my player like this :

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];

But nothing append. Thanks for your help (and sorry for my English :))

I think this line:

NSURL *audioURL = [NSURL URLWithString:[NSString stringWithFormat:@"%@%@",URL_MEDIA,[[allAudioTracks objectAtIndex:i]audio]]];

has to be fileURLWithString instead of URLWithString if you are using a file. Common mistake. Let me know.