concat两个音频文件一个接一个ios

我想将两个音频文件连接成一个.我做了以下代码.请检查下面.

- (BOOL)combineFiles{
    AVMutableComposition *composition = [[AVMutableComposition alloc] init];

    AVMutableCompositionTrack *compositionAudioTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
    [compositionAudioTrack setPreferredVolume:0.8];
    NSString *soundOne  =[[NSBundle mainBundle]pathForResource:@"test1" ofType:@"m4a"];
    NSURL *url = [NSURL fileURLWithPath:soundOne];
    AVAsset *avAsset = [AVURLAsset URLAssetWithURL:url options:nil];
    AVAssetTrack *clipAudioTrack = [[avAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];
    [compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, avAsset.duration) ofTrack:clipAudioTrack atTime:kCMTimeZero error:nil];

    AVMutableCompositionTrack *compositionAudioTrack1 = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
    [compositionAudioTrack1 setPreferredVolume:0.8];
    NSString *soundOne1  =[[NSBundle mainBundle]pathForResource:@"test2" ofType:@"m4a"];
    NSURL *url1 = [NSURL fileURLWithPath:soundOne1];
    AVAsset *avAsset1 = [AVURLAsset URLAssetWithURL:url1 options:nil];
    AVAssetTrack *clipAudioTrack1 = [[avAsset1 tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];
    [compositionAudioTrack1 insertTimeRange:CMTimeRangeMake(kCMTimeZero, avAsset.duration) ofTrack:clipAudioTrack1 atTime:kCMTimeZero error:nil];

    AVAssetExportSession *exportSession = [AVAssetExportSession exportSessionWithAsset:composition presetName:AVAssetExportPresetAppleM4A];
    if (nil == exportSession) return NO;

    exportSession.outputURL = [NSURL fileURLWithPath:[@"test3.m4a" documentDirectory]]; // output path
    exportSession.outputFileType = AVFileTypeAppleM4A; // output file type

    // perform the export
    [exportSession exportAsynchronouslyWithCompletionHandler:^{
        if (AVAssetExportSessionStatusCompleted == exportSession.status) {
            NSLog(@"AVAssetExportSessionStatusCompleted");
        } else if (AVAssetExportSessionStatusFailed == exportSession.status) {
            NSLog(@"AVAssetExportSessionStatusFailed");
        } else {
            NSLog(@"Export Session Status: %ld", (long)exportSession.status);
        }
    }];
    return YES;
}

从上面的代码我们可以将两个音频文件合并为一个,其中两个文件同时播放.但我希望第三个文件一个接一个地播放前两个文件.

请帮我解决这个问题.