создать видео из массива UIImages и сохраните видео в библиотеке iPhone. AVAssetLibrary + AVFoundation

Проблема при сохранении видео в библиотеке iPhone. У меня есть массив UIImages и две кнопки, «convertToVideo» и «saveToiPhoneLib»

-(IBAction) convertToVideo
{
  NSArray *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);

 NSString *documentsDirectory = ([paths count] > 0) ? [paths objectAtIndex:0] : nil;

NSString *savedVideoPath = [documentsDirectory stringByAppendingPathComponent:@"videoOutput"];

printf(" \n\n\n-Video file == %s--\n\n\n",[savedVideoPath UTF8String]);

[self writeImageAsMovie:imageArray toPath:savedVideoPath size:self.view.frame.size duration:3];
}


here i'm passing the imageArray and savedVideoPath to the function below


-(void)writeImageAsMovie:(NSArray *)array toPath:(NSString*)path size:(CGSize)size duration:(int)duration 
{

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


// NSDictionary *bufferAttributes = [NSDictionary dictionaryWithObjectsAndKeys: [NSNumber numberWithInt:kCVPixelFormatType_32ARGB], kCVPixelBufferPixelFormatTypeKey, nil];

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


 NSParameterAssert(writerInput);
 NSParameterAssert([videoWriter canAddInput:writerInput]);
 [videoWriter addInput:writerInput];


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

 CVPixelBufferRef buffer = NULL;

 //convert uiimage to CGImage.

 buffer = [self pixelBufferFromCGImage:[[array objectAtIndex:0] CGImage]];
 [adaptor appendPixelBuffer:buffer withPresentationTime:kCMTimeZero];

 //Write samples:
......


 //Finish the session:
 [writerInput markAsFinished];
 [videoWriter finishWriting];
}


generate a CVPixelBufferRef here


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

    CVReturn status = CVPixelBufferCreate(kCFAllocatorDefault, self.view.frame.size.width,
            self.view.frame.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, self.view.frame.size.width,
             self.view.frame.size.height, 8, 4*self.view.frame.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;
}

сохранение в библиотеке iPhone

-(IBAction) saveToiPhoneLib
{

 NSArray *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);

 NSString *basePath = ([paths count] > 0) ? [paths objectAtIndex:0] : nil;

 NSString *getImagePath = [basePath stringByAppendingPathComponent:@"videoOutput"];

 printf(" \n\n\n-Video file == %s--\n\n\n",[getImagePath UTF8String]);

 UISaveVideoAtPathToSavedPhotosAlbum ( getImagePath,self, @selector(video:didFinishSavingWithError: contextInfo:), nil);
}


- (void) video: (NSString *) videoPath didFinishSavingWithError: (NSError *) error contextInfo: (void *) contextInfo {
 NSLog(@"Finished saving video with error: %@", error);
}

, но при сохранении я получаю сообщение об ошибке: -

Сохранение видео с ошибкой завершено: Error Domain = ALAssetsLibraryErrorDomain Code = -3302 "Invalid data" UserInfo = 0x1d59f0 {NSLocalizedFailureReason = При записи этого ресурса возникла проблема, поскольку данные недействительны, их нельзя просмотреть или воспроизвести. NSLocalizedRecoverySuggestion = Попробуйте использовать другие данные, NSLocalizedDescription = Invalid data}

пожалуйста, дайте мне знать мою ошибку. заранее спасибо