queuePlayer = [[AVQueuePlayer alloc] init];
[queuePlayer insertItem: [AVPlayerItem playerItemWithURL:url] afterItem: nil]; // etc.
[queuePlayer play]

NSArray* tracks = [NSArray arrayWithObjects:@"http://example.com/song1.mp3", @"http://example.com/song2.mp3", @"http://example.com/song3.mp3", nil];

for (NSString* trackName in tracks)
{
    AVURLAsset* audioAsset = [[AVURLAsset alloc]initWithURL:[NSURL URLWithString:trackName]
                                                    options:nil];

    AVMutableCompositionTrack* audioTrack = [_composition addMutableTrackWithMediaType:AVMediaTypeAudio
                                                                      preferredTrackID:kCMPersistentTrackID_Invalid];

    NSError* error;
    [audioTrack insertTimeRange:CMTimeRangeMake([_composition duration], audioAsset.duration)
                        ofTrack:[[audioAsset tracksWithMediaType:AVMediaTypeAudio]objectAtIndex:0]
                         atTime:kCMTimeZero
                          error:&error];

    if (error)
    {
        NSLog(@"%@", [error localizedDescription]);
    }

    // Store the track IDs as track name -> track ID
    [_audioMixTrackIDs setValue:[NSNumber numberWithInteger:audioTrack.trackID]
                         forKey:trackName];

}

_player = [[AVPlayer alloc] initWithPlayerItem:playerItem];

[_player play];