AVCaptureSession只获得了iPhone 3GS的一帧

Question

我有一段代码，设置了从照相机捕获会话使用的OpenCV处理帧，然后从所述帧中设置一个UIImageView的图像特性与所生成的UIImage。当应用程序启动时，图像视图的形象是零，没有帧显示，直到我把堆栈上的另一个视图控制器，然后弹出它关闭。然后，直到我再这样做的图像保持不变。 NSLog的报表显示，回调被称为在接近正确的帧速率。任何想法，为什么不显示？我一路降低帧率到2帧的第二。难道不处理速度不够快？

下面的代码：

- (void)setupCaptureSession {
    NSError *error = nil;

    // Create the session
    AVCaptureSession *session = [[AVCaptureSession alloc] init];

    // Configure the session to produce lower resolution video frames, if your 
    // processing algorithm can cope. We'll specify medium quality for the
    // chosen device.
    session.sessionPreset = AVCaptureSessionPresetLow;

    // Find a suitable AVCaptureDevice
    AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];

    // Create a device input with the device and add it to the session.
    AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device 
                                                                        error:&error];
    if (!input) {
        // Handling the error appropriately.
    }
    [session addInput:input];

    // Create a VideoDataOutput and add it to the session
    AVCaptureVideoDataOutput *output = [[[AVCaptureVideoDataOutput alloc] init] autorelease];
    output.alwaysDiscardsLateVideoFrames = YES;
    [session addOutput:output];

    // Configure your output.
    dispatch_queue_t queue = dispatch_queue_create("myQueue", NULL);
    [output setSampleBufferDelegate:self queue:queue];
    dispatch_release(queue);

    // Specify the pixel format
    output.videoSettings = 
    [NSDictionary dictionaryWithObject:
     [NSNumber numberWithInt:kCVPixelFormatType_32BGRA] 
                                forKey:(id)kCVPixelBufferPixelFormatTypeKey];


    // If you wish to cap the frame rate to a known value, such as 15 fps, set 
    // minFrameDuration.
    output.minFrameDuration = CMTimeMake(1, 1);

    // Start the session running to start the flow of data
    [session startRunning];

    // Assign session to an ivar.
    [self setSession:session];
}

// Create a UIImage from sample buffer data
- (UIImage *) imageFromSampleBuffer:(CMSampleBufferRef) sampleBuffer {
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
    // Lock the base address of the pixel buffer
    CVPixelBufferLockBaseAddress(imageBuffer,0);

    // Get the number of bytes per row for the pixel buffer
    size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer); 
    // Get the pixel buffer width and height
    size_t width = CVPixelBufferGetWidth(imageBuffer); 
    size_t height = CVPixelBufferGetHeight(imageBuffer); 

    // Create a device-dependent RGB color space
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); 
    if (!colorSpace) 
     {
        NSLog(@"CGColorSpaceCreateDeviceRGB failure");
        return nil;
     }

    // Get the base address of the pixel buffer
    void *baseAddress = CVPixelBufferGetBaseAddress(imageBuffer);
    // Get the data size for contiguous planes of the pixel buffer.
    size_t bufferSize = CVPixelBufferGetDataSize(imageBuffer); 

    // Create a Quartz direct-access data provider that uses data we supply
    CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, baseAddress, bufferSize, 
                                                              NULL);
    // Create a bitmap image from data supplied by our data provider
    CGImageRef cgImage = 
    CGImageCreate(width,
                  height,
                  8,
                  32,
                  bytesPerRow,
                  colorSpace,
                  kCGImageAlphaNoneSkipFirst | kCGBitmapByteOrder32Little,
                  provider,
                  NULL,
                  true,
                  kCGRenderingIntentDefault);
    CGDataProviderRelease(provider);
    CGColorSpaceRelease(colorSpace);

    // Create and return an image object representing the specified Quartz image
    UIImage *image = [UIImage imageWithCGImage:cgImage];
    CGImageRelease(cgImage);

    CVPixelBufferUnlockBaseAddress(imageBuffer, 0);

    return image;
}


// Delegate routine that is called when a sample buffer was written
- (void)captureOutput:(AVCaptureOutput *)captureOutput 
didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer 
       fromConnection:(AVCaptureConnection *)connection {
    // Create a UIImage from the sample buffer data
    UIImage *image = [self imageFromSampleBuffer:sampleBuffer];
    [self.delegate cameraCaptureGotFrame:image];
}

Answer 1

这可能与穿线尝试：

[self.delegate performSelectorOnMainThread:@selector(cameraCaptureGotFrame:) withObject:image waitUntilDone:NO];

Answer 2

这看起来像一个线程问题。你不能比主线程更新任何其他线程的意见。在你的设置，这是很好的，委托函数的 captureOutput：didOutputSampleBuffer：的就是所谓的辅助线程。所以，你不能设置从那里图像视图。艺术吉莱斯皮的答案是解决它，如果你能摆脱坏访问错误的一种方式。

另一种方法是修改示例缓冲器 captureOutput：didOutputSampleBuffer：并通过添加 AVCaptureVideoPreviewLayer 实例到您的捕获会话所示。这当然首选的方式，如果你只修改图像的一小部分，如突出的东西。

BTW：可能出现你的坏访问错误，因为你没有在辅助线程保留所创建的图像，所以它会之前被释放的 cameraCaptureGotFrame 的被称为主线程

<强>更新： 为了正确地保留图像，增加的引用计数在 captureOutput：didOutputSampleBuffer：（在次级线程）和在递减它cameraCaptureGotFrame：（在主线程）

// Delegate routine that is called when a sample buffer was written
- (void)captureOutput:(AVCaptureOutput *)captureOutput 
        didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer 
        fromConnection:(AVCaptureConnection *)connection
{
    // Create a UIImage from the sample buffer data
    UIImage *image = [self imageFromSampleBuffer:sampleBuffer];

    // increment ref count
    [image retain];
    [self.delegate performSelectorOnMainThread:@selector(cameraCaptureGotFrame:)
        withObject:image waitUntilDone:NO];

}

- (void) cameraCaptureGotFrame:(UIImage*)image
{
    // whatever this function does, e.g.:
    imageView.image = image;

    // decrement ref count
    [image release];
}

如果你不增加引用计数，图像通过的 cameraCaptureGotFrame前的第二个线程的自动释放池释放：的是所谓的主线程。如果你没有在主线程递减它，图像被永远不会被释放，你的记忆在几秒钟内用完。

Answer 3

您每一个新的图像属性更新后做的一个UIImageView的setNeedsDisplay？

编辑：

在哪里，你什么时候更新的背景图像属性中你的形象有何看法？