audio is not playing after merging two videos into one in Objective C

Question

I want to merge two or more videos into one. I have coded for that and using code below i am able to do so. But, my problem is that after merging two or more videos into one audio is not playing while playing merged video.

So Please, help me for this.

I have added all video url into an array which comes from AppDelegate file.

-(void)MergeVideo
{
    AppDelegate *appdel = (AppDelegate*)[[UIApplication sharedApplication] delegate];

    AVURLAsset *video01;
    AVURLAsset *video02;
    CGFloat totalDuration;
    totalDuration = 0;

    AVMutableComposition *composition = [AVMutableComposition composition];
AVMutableCompositionTrack *composedTrack = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];

    for (int i = 0; i < [appdel.arrVideoPath count]; i++)
    {
        if (i == 0)
        {
            video02 = [[AVURLAsset alloc] initWithURL:[NSURL fileURLWithPath:[appdel.arrVideoPath objectAtIndex:i]] options:nil];

            [composedTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, video02.duration) ofTrack:[[video02 tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] atTime:kCMTimeZero error:nil];
        }
        else
        {
            video01 = [[AVURLAsset alloc] initWithURL:[NSURL fileURLWithPath:[appdel.arrVideoPath objectAtIndex:i-1]] options:nil];
            video02 = [[AVURLAsset alloc] initWithURL:[NSURL fileURLWithPath:[appdel.arrVideoPath objectAtIndex:i]] options:nil];

            float duration1 = CMTimeGetSeconds([video01 duration]);
            totalDuration = totalDuration + duration1;
        CMTime time1 = CMTimeMakeWithSeconds(totalDuration, 1);

            [composedTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, video02.duration) ofTrack:[[video02 tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] atTime:time1 error:nil];
        }

        NSString* documentsDirectory= [self applicationDocumentsDirectory];
        myDocumentPath= [documentsDirectory stringByAppendingPathComponent:@"merge_video.mp4"];
        urlVideoMain = [[NSURL alloc] initFileURLWithPath: myDocumentPath];

        if([[NSFileManager defaultManager] fileExistsAtPath:myDocumentPath])
        {
            [[NSFileManager defaultManager] removeItemAtPath:myDocumentPath error:nil];
        }

        AVAssetExportSession *exporter = [[AVAssetExportSession alloc] initWithAsset:composition presetName:AVAssetExportPresetHighestQuality];
        exporter.outputURL = urlVideoMain;
        exporter.outputFileType = @"com.apple.quicktime-movie";
        exporter.shouldOptimizeForNetworkUse = YES;

        [exporter exportAsynchronouslyWithCompletionHandler:^{

            switch ([exporter status])
            {
                case AVAssetExportSessionStatusFailed:
                    break;

                case AVAssetExportSessionStatusCancelled:
                    break;

                case AVAssetExportSessionStatusCompleted:
                    break;

                default:
                    break;
            }
        }];
    }
}

- (NSString*) applicationDocumentsDirectory
{
    NSArray* paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString* basePath = ([paths count] > 0) ? [paths objectAtIndex:0] : nil;
    return basePath;
}