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

Я пытался записать видео + аудио, используя AVAssetWriter и AVAssetWriterInputs.

Я читал несколько сообщений на этом форуме людей, говорящих, что они смогли это сделать, но это не работает для меня. Если я просто пишу видео, тогда код отлично выполняет свою работу. Когда я добавляю аудио, выходной файл повреждается 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 AVAssetWriterInputs для аудио и видео:

- (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 видеозаписи

- (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, код CaptureOutput

- (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-нибудь мог найти, в чем проблема в этом коде.