iPhone如何设置帧速率和减速AVCapture didOutputSampleBuffer委托

我想减慢iPhone 4S上视频设备的帧速率,这样就不会频繁调用didOutputSampleBuffer委托.这是为了提高性能,因为我处理每个帧并需要一个大框架来处理细节.

我在设置AVSession时尝试使用以下命令:

AVCaptureConnection *conn = [self.output connectionWithMediaType:AVMediaTypeVideo];
[conn setVideoMinFrameDuration:CMTimeMake(1, CAPTURE_FRAMES_PER_SECOND)];
[conn setVideoMaxFrameDuration:CMTimeMake(1, CAPTURE_FRAMES_PER_SECOND)];

但这没有任何效果,我可以将CAPTURE_FRAMES_PER_SECOND从1更改为60,并且看不出性能差异或视频捕获速度减慢.为什么这没效果?如何降低视频设备的捕获帧速率?

我用以下代码设置了Session:

// Define the devices and the session and the settings
self.session = [[AVCaptureSession alloc] init];

//self.session.sessionPreset = AVCaptureSessionPresetPhoto;
//self.session.sessionPreset = AVCaptureSessionPresetHigh;
self.session.sessionPreset = AVCaptureSessionPreset1280x720;

self.device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
self.input = [AVCaptureDeviceInput deviceInputWithDevice:self.device error:nil];

// Add the video frame output
self.output = [[AVCaptureVideoDataOutput alloc] init];
[self.output setAlwaysDiscardsLateVideoFrames:YES];
self.output.videoSettings = [NSDictionary dictionaryWithObject:[NSNumber numberWithInt:kCVPixelFormatType_32BGRA]
                                                        forKey:(id)kCVPixelBufferPixelFormatTypeKey];

// A dispatch queue to get frames
dispatch_queue_t queue;
queue = dispatch_queue_create("frame_queue", NULL);

// Setup the frame rate    
AVCaptureConnection *conn = [self.output connectionWithMediaType:AVMediaTypeVideo];
[conn setVideoMinFrameDuration:CMTimeMake(1, CAPTURE_FRAMES_PER_SECOND)];
[conn setVideoMaxFrameDuration:CMTimeMake(1, CAPTURE_FRAMES_PER_SECOND)];

// Setup input and output and set the delegate to self
[self.output setSampleBufferDelegate:self queue:queue];
[self.session addInput:self.input];
[self.session addOutput:self.output];

// Start the session
[self.session startRunning];

我使用下面的“didOutputSampleBuffer”委托实现捕获帧:

// The delegate method where we get our image data frames from
- (void)captureOutput:(AVCaptureOutput *)captureOutput
didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer
       fromConnection:(AVCaptureConnection *)connection
{

    // Extract a UImage
    CVPixelBufferRef pixel_buffer = CMSampleBufferGetImageBuffer(sampleBuffer);
    CIImage *ciImage = [CIImage imageWithCVPixelBuffer:pixel_buffer];

    // Capture the image
    CGImageRef ref = [self.context createCGImage:ciImage fromRect:ciImage.extent];

    // This sets the captured image orientation correctly
    UIImage *image = [UIImage imageWithCGImage:ref scale:1.0 orientation:UIImageOrientationLeft];

    // Release the CGImage
    CGImageRelease(ref);

    // Update the UI on the main thread but throttle the processing
    [self performSelectorOnMainThread:@selector(updateUIWithCapturedImageAndProcessWithImage:) withObject:image waitUntilDone:YES];

}

最佳答案 我不确定你在运行什么iOS,但是像这样包含你的代码:

AVCaptureConnection *conn = [self.output connectionWithMediaType:AVMediaTypeVideo];
if ([conn isVideoMaxFrameDurationSupported] && [conn isVideoMinFrameDurationSupported])
{
  [conn setVideoMinFrameDuration:CMTimeMake(1, CAPTURE_FRAMES_PER_SECOND)];
  [conn setVideoMaxFrameDuration:CMTimeMake(1, CAPTURE_FRAMES_PER_SECOND)];
}

else
  NSLog(@"Setting Max and/or Min frame duration is unsupported";

然后从那里去.我怀疑它在iOS上不受支持.

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