Merging audio and video file in ios - 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