Necesito guardar algunos fotogramas de video de una sesión de captura en la memoria y escribirlos en un archivo cuando sucede 'algo'.

Similar aesta solució, uso este código para poner un marco en un NSMutableArray:

- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection*)connection
{       
    //...
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
    uint8 *baseAddress = (uint8*)CVPixelBufferGetBaseAddress(imageBuffer);
    NSData *rawFrame = [[NSData alloc] initWithBytes:(void*)baseAddress length:(height * bytesPerRow)];
    [m_frameDataArray addObject:rawFrame];
    [rawFrame release];
    //...
}

Y esto para escribir el archivo de video:

-(void)writeFramesToFile
{
    //...
    NSDictionary *outputSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                                    [NSNumber numberWithInt:640], AVVideoWidthKey,
                                    [NSNumber numberWithInt:480], AVVideoHeightKey,
                                    AVVideoCodecH264, AVVideoCodecKey,
                                    nil ];
    AVAssetWriterInput *bufferAssetWriterInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:outputSettings];
    AVAssetWriter *bufferAssetWriter = [[AVAssetWriter alloc]initWithURL:pathURL fileType:AVFileTypeQuickTimeMovie error:&error];
    [bufferAssetWriter addInput:bufferAssetWriterInput];

    [bufferAssetWriter startWriting];
    [bufferAssetWriter startSessionAtSourceTime:startTime];
    for (NSInteger i = 1; i < m_frameDataArray.count; i++){
        NSData *rawFrame = [m_frameDataArray objectAtIndex:i];
        CVImageBufferRef imgBuf = [rawFrame bytes];
        [pixelBufferAdaptor appendPixelBuffer:imgBuf withPresentationTime:CMTimeMake(1,10)]; //<-- EXC_BAD_ACCESS
        [rawFrame release];
    }
    //... (finishing video file)
}

Pero algo está mal con la referencia imgBuf. ¿Alguna sugerencia? Gracias por adelantado