Concat two audio files (one after another) in iOS

I want to concatenate two audio files into one. I had done following code. Please check below.

- (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;
}

From above code we can combine two audio files into one, where both files play simultaneously. But I want the third file to play the first two files one after the other.

Please help me to solve this problem.

After doing much research I found answer.. It works..

- (void)mergeTwoAudioFiles{
    AVAsset *avAsset1 = [AVURLAsset URLAssetWithURL:[NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:@"test1" ofType:@"m4a"]] options:nil];
    AVAsset *avAsset2 = [AVURLAsset URLAssetWithURL:[NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:@"test2" ofType:@"m4a"]] options:nil];

    AVMutableComposition *composition = [[AVMutableComposition alloc] init];
    [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];

    AVMutableCompositionTrack *track = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
    AVAssetTrack *assetTrack1 = [[avAsset1 tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];
    AVAssetTrack *assetTrack2 = [[avAsset2 tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];

    CMTime insertionPoint = kCMTimeZero;
    [track insertTimeRange:CMTimeRangeMake(kCMTimeZero, avAsset1.duration) ofTrack:assetTrack1 atTime:insertionPoint error:nil];
    insertionPoint = CMTimeAdd(insertionPoint, avAsset1.duration);
    [track insertTimeRange:CMTimeRangeMake(kCMTimeZero, avAsset2.duration) ofTrack:assetTrack2 atTime:insertionPoint error:nil];

    AVAssetExportSession *exportSession = [AVAssetExportSession exportSessionWithAsset:composition presetName:AVAssetExportPresetAppleM4A];
    exportSession.outputURL = [NSURL fileURLWithPath:[@"test3.m4a" documentDirectory]];
    exportSession.outputFileType = AVFileTypeAppleM4A;

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