AVFoundation + AssetWriter: Generate Movie With Images and Audio

I ended up exporting the video separately using the above code and added the audio files separately using AVComposition & AVExportSession.
Here is the code

-(void) addAudioToFileAtPath:(NSString *) filePath toPath:(NSString *)outFilePath
{
    NSError * error = nil;

    AVMutableComposition * composition = [AVMutableComposition composition];


    AVURLAsset * videoAsset = [AVURLAsset URLAssetWithURL:[NSURL fileURLWithPath:filePath] options:nil];

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

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

    [compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero,videoAsset.duration) ofTrack:videoAssetTrack atTime:kCMTimeZero
                                     error:&error];     

    CMTime audioStartTime = kCMTimeZero;
    for (NSDictionary * audioInfo in audioInfoArray)
    {
        NSString * pathString = [audioInfo objectForKey:audioFilePath];
        AVURLAsset * urlAsset = [AVURLAsset URLAssetWithURL:[NSURL fileURLWithPath:pathString] options:nil];

        AVAssetTrack * audioAssetTrack = [[urlAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];
        AVMutableCompositionTrack *compositionAudioTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio 
                                                                                    preferredTrackID: kCMPersistentTrackID_Invalid];

        [compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero,urlAsset.duration) ofTrack:audioAssetTrack atTime:audioStartTime error:&error];      

        audioStartTime = CMTimeAdd(audioStartTime, CMTimeMake((int) (([[audioInfo objectForKey:audioDuration] floatValue] * kRecordingFPS) + 0.5), kRecordingFPS));
    }
    AVAssetExportSession* assetExport = [[AVAssetExportSession alloc] initWithAsset:composition presetName:AVAssetExportPresetMediumQuality];  
    assetExport.videoComposition = mutableVideoComposition;

    assetExport.outputFileType =AVFileTypeQuickTimeMovie;// @"com.apple.quicktime-movie";
    assetExport.outputURL = [NSURL fileURLWithPath:outFilePath];

    [assetExport exportAsynchronouslyWithCompletionHandler:
     ^(void ) {
         switch (assetExport.status) 
         {
             case AVAssetExportSessionStatusCompleted:
//                export complete 
                 NSLog(@"Export Complete");
                 break;
             case AVAssetExportSessionStatusFailed:
                 NSLog(@"Export Failed");
                 NSLog(@"ExportSessionError: %@", [assetExport.error localizedDescription]);
//                export error (see exportSession.error)  
                 break;
             case AVAssetExportSessionStatusCancelled:
                 NSLog(@"Export Failed");
                 NSLog(@"ExportSessionError: %@", [assetExport.error localizedDescription]);
//                export cancelled  
                 break;
         }
     }];    
}