Этот код для записи видео+аудио через AVAssetWriter и AVAssetWriterInputs не работает. Зачем?

Я пытался написать видео + аудио с помощью AVAssetWriter и AVAssetWriterInputs.

Я прочитал несколько сообщений на этом форуме людей, говорящих, что они смогли это сделать, но это не работает для меня.
Если я просто пишу видео, то код делает свою работу очень хорошо. Когда я добавляю аудио, выходной файл поврежден и не может быть воспроизведен.

вот часть моего кода:

настройка AVCaptureVideoDataOutput и AVCaptureAudioDataOutput:

NSError *error = nil;



// Setup the video input

AVCaptureDevice *videoDevice = [AVCaptureDevice defaultDeviceWithMediaType: AVMediaTypeVideo];

// Create a device input with the device and add it to the session.

AVCaptureDeviceInput *videoInput = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:&error];

// Setup the video output

_videoOutput = [[AVCaptureVideoDataOutput alloc] init];

_videoOutput.alwaysDiscardsLateVideoFrames = NO;

_videoOutput.videoSettings =

[NSDictionary dictionaryWithObject:

[NSNumber numberWithInt:kCVPixelFormatType_32BGRA] forKey:(id)kCVPixelBufferPixelFormatTypeKey];     



// Setup the audio input

AVCaptureDevice *audioDevice     = [AVCaptureDevice defaultDeviceWithMediaType: AVMediaTypeAudio];

AVCaptureDeviceInput *audioInput = [AVCaptureDeviceInput deviceInputWithDevice:audioDevice error:&error ];     

// Setup the audio output

_audioOutput = [[AVCaptureAudioDataOutput alloc] init];



// Create the session

_capSession = [[AVCaptureSession alloc] init];

[_capSession addInput:videoInput];

[_capSession addInput:audioInput];

[_capSession addOutput:_videoOutput];

[_capSession addOutput:_audioOutput];



_capSession.sessionPreset = AVCaptureSessionPresetLow;     



// Setup the queue

dispatch_queue_t queue = dispatch_queue_create("MyQueue", NULL);

[_videoOutput setSampleBufferDelegate:self queue:queue];

[_audioOutput setSampleBufferDelegate:self queue:queue];

dispatch_release(queue);

настройка AVAssetWriter и связывание с ним аудио и видео AVAssetWriterInputs:

- (BOOL)setupWriter {

    NSError *error = nil;

    _videoWriter = [[AVAssetWriter alloc] initWithURL:videoURL 

                                             fileType:AVFileTypeQuickTimeMovie

                                                error:&error];

    NSParameterAssert(_videoWriter);





    // Add video input

    NSDictionary *videoCompressionProps = [NSDictionary dictionaryWithObjectsAndKeys:

                                                 [NSNumber numberWithDouble:128.0*1024.0], AVVideoAverageBitRateKey,

                                                        nil ];



    NSDictionary *videoSettings = [NSDictionary dictionaryWithObjectsAndKeys:

                                              AVVideoCodecH264, AVVideoCodecKey,

                                              [NSNumber numberWithInt:192], AVVideoWidthKey,

                                              [NSNumber numberWithInt:144], AVVideoHeightKey,

                                              videoCompressionProps, AVVideoCompressionPropertiesKey,

                                              nil];



    _videoWriterInput = [[AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo

                                                            outputSettings:videoSettings] retain];





    NSParameterAssert(_videoWriterInput);

    _videoWriterInput.expectsMediaDataInRealTime = YES;





    // Add the audio input

    AudioChannelLayout acl;

    bzero( &acl, sizeof(acl));

    acl.mChannelLayoutTag = kAudioChannelLayoutTag_Mono;





    NSDictionary* audioOutputSettings = nil;          

    // Both type of audio inputs causes output video file to be corrupted.

    if (NO) {

        // should work from iphone 3GS on and from ipod 3rd generation

        audioOutputSettings = [NSDictionary dictionaryWithObjectsAndKeys:

                              [ NSNumber numberWithInt: kAudioFormatMPEG4AAC ], AVFormatIDKey,

                                     [ NSNumber numberWithInt: 1 ], AVNumberOfChannelsKey,

                              [ NSNumber numberWithFloat: 44100.0 ], AVSampleRateKey,

                              [ NSNumber numberWithInt: 64000 ], AVEncoderBitRateKey,

                              [ NSData dataWithBytes: &acl length: sizeof( acl ) ], AVChannelLayoutKey,

                              nil];

    } else {

        // should work on any device requires more space

        audioOutputSettings = [ NSDictionary dictionaryWithObjectsAndKeys:                       

                              [ NSNumber numberWithInt: kAudioFormatAppleLossless ], AVFormatIDKey,

                                    [ NSNumber numberWithInt: 16 ], AVEncoderBitDepthHintKey,

                              [ NSNumber numberWithFloat: 44100.0 ], AVSampleRateKey,

                              [ NSNumber numberWithInt: 1 ], AVNumberOfChannelsKey,                                      

                              [ NSData dataWithBytes: &acl length: sizeof( acl ) ], AVChannelLayoutKey,

                                 nil ];

    } 



    _audioWriterInput = [[AVAssetWriterInput 

                            assetWriterInputWithMediaType: AVMediaTypeAudio 

                  outputSettings: audioOutputSettings ] retain];



    _audioWriterInput.expectsMediaDataInRealTime = YES;



    // add input

    [_videoWriter addInput:_videoWriterInput];

    [_videoWriter addInput:_audioWriterInput];



    return YES;

}

вот функции для запуска / остановки записи видео

- (void)startVideoRecording

{

    if (!_isRecording) {

        NSLog(@"start video recording...");

        if (![self setupWriter]) {

             return;

        }

        _isRecording = YES;

    }

}



- (void)stopVideoRecording

{

    if (_isRecording) {

        _isRecording = NO;



        [_videoWriterInput markAsFinished];

        [_videoWriter endSessionAtSourceTime:lastSampleTime];



        [_videoWriter finishWriting];



        NSLog(@"video recording stopped");

    }

}

и, наконец, CaptureOutput код

- (void)captureOutput:(AVCaptureOutput *)captureOutput

didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer

       fromConnection:(AVCaptureConnection *)connection

{

    if (!CMSampleBufferDataIsReady(sampleBuffer)) {

        NSLog( @"sample buffer is not ready. Skipping sample" );

        return;

    }





    if (_isRecording == YES) {

        lastSampleTime = CMSampleBufferGetPresentationTimeStamp(sampleBuffer);

        if (_videoWriter.status != AVAssetWriterStatusWriting ) {

            [_videoWriter startWriting];

            [_videoWriter startSessionAtSourceTime:lastSampleTime];

        }



        if (captureOutput == _videoOutput) {

            [self newVideoSample:sampleBuffer];

        }



        /*

        // If I add audio to the video, then the output file gets corrupted and it cannot be reproduced

        } else {

            [self newAudioSample:sampleBuffer];

        }

    */

    }

}



- (void)newVideoSample:(CMSampleBufferRef)sampleBuffer

{     

    if (_isRecording) {

        if (_videoWriter.status > AVAssetWriterStatusWriting) {

             NSLog(@"Warning: writer status is %d", _videoWriter.status);

             if (_videoWriter.status == AVAssetWriterStatusFailed)

                  NSLog(@"Error: %@", _videoWriter.error);

             return;

        }



        if (![_videoWriterInput appendSampleBuffer:sampleBuffer]) {

             NSLog(@"Unable to write to video input");

        }

    }

}







- (void)newAudioSample:(CMSampleBufferRef)sampleBuffer

{     

    if (_isRecording) {

        if (_videoWriter.status > AVAssetWriterStatusWriting) {

             NSLog(@"Warning: writer status is %d", _videoWriter.status);

             if (_videoWriter.status == AVAssetWriterStatusFailed)

                  NSLog(@"Error: %@", _videoWriter.error);

             return;

        }



        if (![_audioWriterInput appendSampleBuffer:sampleBuffer]) {

             NSLog(@"Unable to write to audio input");

        }

    }

}

Я был бы очень рад, если бы кто-то мог найти, в чем проблема в этом коде.