AVFoundation + AssetWriter: создание фильма с изображениями и аудио

Мне нужно экспортировать фильм из моего приложения для iPhone, который содержит UIImage из NSArray, и добавить несколько аудиофайлов в формате .caf, которые должны запускаться в заранее определенное время. Now I have been able to use the AVAssetWriter (after going through many questions and answers on this and other sites) to export the video portion containing the images but cant seem to find a way to add the audio files to complete the movie.

Here is what I have gotten so far

-(void) writeImagesToMovieAtPath:(NSString *) path withSize:(CGSize) size
{
    NSLog(@"Write Started");

    NSError *error = nil;

    AVAssetWriter *videoWriter = [[AVAssetWriter alloc] initWithURL:
                              [NSURL fileURLWithPath:path] fileType:AVFileTypeQuickTimeMovie
                                                          error:&error];    
    NSParameterAssert(videoWriter);

    NSDictionary *videoSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                               AVVideoCodecH264, AVVideoCodecKey,
                               [NSNumber numberWithInt:size.width], AVVideoWidthKey,
                               [NSNumber numberWithInt:size.height], AVVideoHeightKey,
                               nil];

    AVAssetWriterInput* videoWriterInput = [[AVAssetWriterInput
                                    assetWriterInputWithMediaType:AVMediaTypeVideo
                                    outputSettings:videoSettings] retain];


    AVAssetWriterInputPixelBufferAdaptor *adaptor = [AVAssetWriterInputPixelBufferAdaptor
                                            assetWriterInputPixelBufferAdaptorWithAssetWriterInput:videoWriterInput
                                                 sourcePixelBufferAttributes:nil];

    NSParameterAssert(videoWriterInput);
    NSParameterAssert([videoWriter canAddInput:videoWriterInput]);
    videoWriterInput.expectsMediaDataInRealTime = YES;
    [videoWriter addInput:videoWriterInput];

    //Start a session:
    [videoWriter startWriting];
    [videoWriter startSessionAtSourceTime:kCMTimeZero];

    CVPixelBufferRef buffer = NULL;

    //convert uiimage to CGImage.

    int frameCount = 0;

    for(UIImage * img in imageArray)
    {
            buffer = [self pixelBufferFromCGImage:[img CGImage] andSize:size];

            BOOL append_ok = NO;
            int j = 0;
            while (!append_ok && j < 30) 
            {
                if (adaptor.assetWriterInput.readyForMoreMediaData) 
                {
                    printf("appending %d attemp %d\n", frameCount, j);

                    CMTime frameTime = CMTimeMake(frameCount,(int32_t) kRecordingFPS);
                    append_ok = [adaptor appendPixelBuffer:buffer withPresentationTime:frameTime];

                    if(buffer)
                        CVBufferRelease(buffer);
                    [NSThread sleepForTimeInterval:0.05];
                } 
                else 
                {
                    printf("adaptor not ready %d, %d\n", frameCount, j);
                    [NSThread sleepForTimeInterval:0.1];
                }
                j++;
            }
            if (!append_ok) {
                printf("error appending image %d times %d\n", frameCount, j);
            }
            frameCount++;
        }
    }

    //Finish the session:
    [videoWriterInput markAsFinished];  
    [videoWriter finishWriting];
    NSLog(@"Write Ended");
}

And now the code for pixelBufferFromCGImage

- (CVPixelBufferRef) pixelBufferFromCGImage: (CGImageRef) image andSize:(CGSize) size
{
    NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
                         [NSNumber numberWithBool:YES], kCVPixelBufferCGImageCompatibilityKey,
                         [NSNumber numberWithBool:YES], kCVPixelBufferCGBitmapContextCompatibilityKey,
                         nil];
    CVPixelBufferRef pxbuffer = NULL;

    CVReturn status = CVPixelBufferCreate(kCFAllocatorDefault, size.width,
                                      size.height, kCVPixelFormatType_32ARGB, (CFDictionaryRef) options, 
                                      &pxbuffer);
    NSParameterAssert(status == kCVReturnSuccess && pxbuffer != NULL);

    CVPixelBufferLockBaseAddress(pxbuffer, 0);
    void *pxdata = CVPixelBufferGetBaseAddress(pxbuffer);
    NSParameterAssert(pxdata != NULL);

    CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(pxdata, size.width,
                                             size.height, 8, 4*size.width, rgbColorSpace, 
                                             kCGImageAlphaNoneSkipFirst);
    NSParameterAssert(context);
    CGContextConcatCTM(context, CGAffineTransformMakeRotation(0));
    CGContextDrawImage(context, CGRectMake(0, 0, CGImageGetWidth(image), 
                                           CGImageGetHeight(image)), image);
    CGColorSpaceRelease(rgbColorSpace);
    CGContextRelease(context);

    CVPixelBufferUnlockBaseAddress(pxbuffer, 0);

    return pxbuffer;
}

So can you help me out regarding how to add the audio files and how to make buffers for them and the adaptor and input settings etc

If this approach might cause a problem guide me about how to use a AVMutableComposition to use the image array for video export