Проблема с преобразованием массива изображений в файл MP4

У меня есть массив изображений, который преобразуется в файл MP4. Из того, что я могу сказать, не похоже, что изображения добавляются к видеокадру для видео, что приводит к нулевым кадрам в видео. Как мне исправить эту ошибку, чтобы правильно преобразовать изображения в видеофайл? Ниже приведен весь код конвертера и изображения сообщений об ошибках.

- (void) createVideoPlayer:(NSArray *)imagesArray {

    NSError *error = nil;


    // set up file manager, and file videoOutputPath, remove "test_output.mp4" if it exists...
    //NSString *videoOutputPath = @"/Users/someuser/Desktop/test_output.mp4";
    NSFileManager *fileMgr = [NSFileManager defaultManager];
    NSString *documentsDirectory = [NSHomeDirectory()
                                stringByAppendingPathComponent:@"Documents"];
    NSString *videoOutputPath = [documentsDirectory stringByAppendingPathComponent:@"test_output.mp4"];
    //NSLog(@"-->videoOutputPath= %@", videoOutputPath);
    // get rid of existing mp4 if exists...
    if ([fileMgr removeItemAtPath:videoOutputPath error:&error] != YES)
        NSLog(@"Unable to delete file: %@", [error localizedDescription]);


    CGSize imageSize = CGSizeMake(640, 853);


//////////////     end setup    ///////////////////////////////////

    NSLog(@"Start building video from defined frames.");

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



    NSDictionary* compression = @{
                              AVVideoAverageBitRateKey:[NSNumber numberWithInt:(960000 * 2)],
                              AVVideoMaxKeyFrameIntervalKey:[NSNumber numberWithInt:1]
                              };
    AVAssetWriterInput* videoWriterInput = [AVAssetWriterInput
                                        assetWriterInputWithMediaType:AVMediaTypeVideo
                                        outputSettings:@{
                                                         AVVideoCodecKey:AVVideoCodecH264,
                                                         AVVideoCompressionPropertiesKey:compression,
                                                         AVVideoWidthKey:[NSNumber numberWithInt:imageSize.width],
                                                         AVVideoHeightKey:[NSNumber numberWithInt:imageSize.height]
                                                         }];


    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;

  //  double FPS = self.numberOfImages / 10;

    //for(VideoFrame * frm in imageArray)
    NSLog(@"**************************************************");
    for(UIImage * img in imagesArray)
    {
        //UIImage * img = frm._imageFrame;
        buffer = [self pixelBufferFromCGImage:[img CGImage]];

        BOOL append_ok = NO;
        int j = 0;
        while (!append_ok && j < 30) {
            if (adaptor.assetWriterInput.readyForMoreMediaData)  {
                //print out status:
                NSLog(@"Processing video frame (%d,%lu)",frameCount,(unsigned long)[imagesArray count]);

                CMTime frameTime = CMTimeMake(frameCount,(int32_t) 10);
                append_ok = [adaptor appendPixelBuffer:buffer withPresentationTime:frameTime];
                if(!append_ok){
                    NSError *error = videoWriter.error;
                    if(error!=nil) {
                        NSLog(@"Unresolved error %@,%@.", error, [error userInfo]);
                    }
                }
            }
            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, with error.", frameCount, j);
        }
        frameCount++;
    }
    NSLog(@"**************************************************");

    //Finish the session:
    [videoWriterInput markAsFinished];
    [videoWriter finishWritingWithCompletionHandler:^{

    }];
    NSLog(@"Write Ended");




    AVMutableComposition* mixComposition = [AVMutableComposition composition];



    // this is the video file that was just written above, full path to file is in --> videoOutputPath
    NSURL    *video_inputFileUrl = [NSURL fileURLWithPath:videoOutputPath];
    NSLog(@"%@", video_inputFileUrl);
    // create the final video output file as MP4
    NSString *outputFilePath = [documentsDirectory stringByAppendingPathComponent:@"final_video.mp4"];
    NSURL    *outputFileUrl = [NSURL fileURLWithPath:outputFilePath];
    NSLog(@"%@", outputFileUrl);
    if ([[NSFileManager defaultManager] fileExistsAtPath:outputFilePath])
        [[NSFileManager defaultManager] removeItemAtPath:outputFilePath error:nil];

    CMTime nextClipStartTime = kCMTimeZero;

    AVURLAsset *videoAsset = [[AVURLAsset alloc] initWithURL:video_inputFileUrl options:nil];
    CMTimeRange video_timeRange = CMTimeRangeMake(kCMTimeZero,videoAsset.duration);

    AVMutableCompositionTrack *a_compositionVideoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
    [a_compositionVideoTrack insertTimeRange:video_timeRange ofTrack:[[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] atTime:nextClipStartTime error:nil];

    //nextClipStartTime = CMTimeAdd(nextClipStartTime, a_timeRange.duration);

    //AVURLAsset* audioAsset = [[AVURLAsset alloc]initWithURL:audio_inputFileUrl options:nil];
    //CMTimeRange audio_timeRange = CMTimeRangeMake(kCMTimeZero, audioAsset.duration);
   // AVMutableCompositionTrack *b_compositionAudioTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
   // [b_compositionAudioTrack insertTimeRange:audio_timeRange ofTrack:[[audioAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0] atTime:nextClipStartTime error:nil];



    AVAssetExportSession* _assetExport = [[AVAssetExportSession alloc] initWithAsset:mixComposition presetName:AVAssetExportPresetHighestQuality];

    _assetExport.outputFileType = @"public.mpeg-4";
    //NSLog(@"support file types= %@", [_assetExport supportedFileTypes]);
    _assetExport.outputURL = outputFileUrl;
    theURL = _assetExport.outputURL;
    [_assetExport exportAsynchronouslyWithCompletionHandler:
     ^(void ) {


         dispatch_async(dispatch_get_main_queue(), ^{

             [spinner stopAnimating];

         moviePlayer = [[MPMoviePlayerController alloc] initWithContentURL:_assetExport.outputURL];
         [moviePlayer.view setFrame:CGRectMake(0, 100, 320, 320)];
         [moviePlayer prepareToPlay];
         [moviePlayer repeatMode];
          moviePlayer.backgroundView.backgroundColor = [UIColor whiteColor];
         // And other options you can look through the documentation.
         [self.view addSubview:moviePlayer.view];
         [moviePlayer play];



         });
     }
     ];

    NSLog(@"DONE.....outputFilePath--->%@", outputFilePath);


        ////////////////////////////////////////////////////////////////////////////
        ////////////////////////////////////////////////////////////////////////////

}


////////////////////////
- (CVPixelBufferRef) pixelBufferFromCGImage: (CGImageRef) image {


    CGSize size = CGSizeMake(640, 853);

    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,
                                      (__bridge CFDictionaryRef) options,
                                      &pxbuffer);
    if (status != kCVReturnSuccess){
        NSLog(@"Failed to create pixel buffer");
    }

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

    CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(pxdata, size.width,
                                             size.height, 8, 4*size.width, rgbColorSpace,
                                             kCGImageAlphaNoneSkipFirst);


    CGContextConcatCTM(context, CGAffineTransformMakeRotation(0));
    CGContextDrawImage(context, CGRectMake(0, 0, CGImageGetWidth(image),
                                       CGImageGetHeight(image)), image);

    CGColorSpaceRelease(rgbColorSpace);
    CGContextRelease(context);

    CVPixelBufferUnlockBaseAddress(pxbuffer, 0);

    return pxbuffer; 

}