Merging audio and video file in ios

Question

I am trying to merge Audio and Video file, below is my code :

AVURLAsset* audioAsset = [[AVURLAsset alloc]initWithURL:_BAckgroungMusicFileURL options:nil];

AVURLAsset* videoAsset = [AVURLAsset URLAssetWithURL:[NSURL fileURLWithPath:_AppDel._RecordedVideoPath] options:nil];

AVMutableComposition* composition = [AVMutableComposition composition];

AVMutableVideoComposition *videoComposition = [AVMutableVideoComposition videoComposition];
videoComposition.frameDuration = CMTimeMake(1,24);
videoComposition.renderScale = 1.0;


AVMutableCompositionTrack *compositionCommentaryTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio
                                                                                 preferredTrackID:kCMPersistentTrackID_Invalid];
[compositionCommentaryTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, videoAsset.duration)
                                    ofTrack:[[audioAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0]
                                     atTime:kCMTimeZero error:nil];

AVMutableCompositionTrack *compositionVideoTrack = [composition addMutableTrackWithMediaType:AVMediaTypeVideo
                                                                            preferredTrackID:kCMPersistentTrackID_Invalid];
[compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, videoAsset.duration)
                               ofTrack:[[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0]
                                atTime:kCMTimeZero error:nil];


AVMutableVideoCompositionInstruction *instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];

AVMutableVideoCompositionLayerInstruction *layerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:compositionVideoTrack];

AVAssetTrack *sourceVideoTrack = [[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];


CGAffineTransform rotationTransform = CGAffineTransformMakeRotation(M_PI/2);
CGAffineTransform rotateTranslate = CGAffineTransformTranslate(rotationTransform,320,0);

[compositionVideoTrack setPreferredTransform:sourceVideoTrack.preferredTransform];
[layerInstruction setTransform:rotateTranslate atTime:kCMTimeZero];

instruction.layerInstructions = [NSArray arrayWithObject: layerInstruction];
videoComposition.instructions = [NSArray arrayWithObject: instruction];

AVAssetExportSession* _assetExport = [[AVAssetExportSession alloc] initWithAsset:composition
                                                                      presetName:AVAssetExportPresetPassthrough];
NSDate *_TodayDate = [NSDate dateWithTimeIntervalSinceNow:0];
_CalenderDate = [_TodayDate description];
_CombinedVideoPath = [NSString stringWithFormat:@"%@/%@.mov", DOCUMENTS_FOLDER, _CalenderDate] ;

NSURL *exportUrl = [NSURL fileURLWithPath:_CombinedVideoPath];


_assetExport.outputFileType = @"com.apple.quicktime-movie";
NSLog(@"file type %@",_assetExport.outputFileType);
_assetExport.outputURL = exportUrl;
_assetExport.shouldOptimizeForNetworkUse = YES;

[_assetExport exportAsynchronouslyWithCompletionHandler:
 ^(void ) {
     switch (_assetExport.status)
     {
         case AVAssetExportSessionStatusCompleted:
             NSLog(@"AVAssetExportSessionStatusCompleted");
             [self SaveVideo];
             break;
         case AVAssetExportSessionStatusFailed:
             NSLog(@"Export Failed");
             NSLog(@"ExportSessionError: %@", [_assetExport.error localizedDescription]);
             [self mergingCompleted];
             break;
         case AVAssetExportSessionStatusCancelled:
             [self mergingCompleted];
             NSLog(@"Export Session Status: %d", _assetExport.status);
             NSLog(@"Export Failed");
             NSLog(@"ExportSessionError: %@", [_assetExport.error localizedDescription]);

             break;
     }
 }];

Here the video to be merged is recorded video. But my problem is that, when I am trying to merge this audio and video the resultant video contains the recorded video and the audio. It does not contain the audio of the recorded video. How can I have the video its audio to be merged with another audio.

Any help will be appreciated.

Thanks in advance