Question

我正在使用此代码捕获图像

#pragma mark - image capture

// Create and configure a capture session and start it running
- (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 = AVCaptureSessionPresetMedium;

    // 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)
    {
        NSLog(@"PANIC: no media input");
    }
    [session addInput:input];

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

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

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




// Delegate routine that is called when a sample buffer was written
- (void)captureOutput:(AVCaptureOutput *)captureOutput 
didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer 
   fromConnection:(AVCaptureConnection *)connection
{ 
    NSLog(@"captureOutput: didOutputSampleBufferFromConnection");

    // Create a UIImage from the sample buffer data
    UIImage *image = [self imageFromSampleBuffer:sampleBuffer];

    //< Add your code here that uses the image >
    [self.imageView setImage:image];
    [self.view setNeedsDisplay];
}


// Create a UIImage from sample buffer data
- (UIImage *) imageFromSampleBuffer:(CMSampleBufferRef) sampleBuffer 
{
    NSLog(@"imageFromSampleBuffer: called");
    // Get a CMSampleBuffer's Core Video image buffer for the media data
    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
    void *baseAddress = CVPixelBufferGetBaseAddress(imageBuffer); 

    // 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(); 

    // Create a bitmap graphics context with the sample buffer data
    CGContextRef context = CGBitmapContextCreate(baseAddress, width, height, 8, 
                                             bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst); 
    // Create a Quartz image from the pixel data in the bitmap graphics context
    CGImageRef quartzImage = CGBitmapContextCreateImage(context); 
    // Unlock the pixel buffer
    CVPixelBufferUnlockBaseAddress(imageBuffer,0);


    // Free up the context and color space
    CGContextRelease(context); 
    CGColorSpaceRelease(colorSpace);

    // Create an image object from the Quartz image
    UIImage *image = [UIImage imageWithCGImage:quartzImage];

    // Release the Quartz image
    CGImageRelease(quartzImage);

    return (image);
}

-(void)setSession:(AVCaptureSession *)session
{
    NSLog(@"setting session...");
    self.captureSession=session;
}

捕获代码有效。但！我需要改变一些事情： - 在我看来，来自相机的视频流。 - 从中获取图像（例如5秒）。请帮帮我，怎么办呢？

Answer 1

添加以下行

output.minFrameDuration = CMTimeMake(5, 1);

在评论下面

 // If you wish to cap the frame rate to a known value, such as 15 fps, set
 // minFrameDuration.

但高于

[session startRunning];

修改

使用以下代码预览相机输出。

AVCaptureVideoPreviewLayer *previewLayer = [AVCaptureVideoPreviewLayer layerWithSession:session]; UIView *aView = self.view; CGRect videoRect = CGRectMake(0.0, 0.0, 320.0, 150.0); previewLayer.frame = videoRect; // Assume you want the preview layer to fill the view. [aView.layer addSublayer:previewLayer];

编辑2： 好的..

Apple提供了一种设置minFrameDuration here
的方法
现在，使用以下代码设置帧持续时间

AVCaptureConnection *conn = [output connectionWithMediaType:AVMediaTypeVideo]; if (conn.supportsVideoMinFrameDuration) conn.videoMinFrameDuration = CMTimeMake(5,1); if (conn.supportsVideoMaxFrameDuration) conn.videoMaxFrameDuration = CMTimeMake(5,1);

Answer 2

小心 - 来自AVCaptureOutput的回调发布在您指定的调度队列中。我看到你从这个回调中执行UI更新，这是错误的。您应该只在主队列中执行它们。 E.g。

- (void)captureOutput:(AVCaptureOutput *)captureOutput 
    didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer 
       fromConnection:(AVCaptureConnection *)connection
{ 
    NSLog(@"captureOutput: didOutputSampleBufferFromConnection");
    // Create a UIImage from the sample buffer data
    UIImage *image = [self imageFromSampleBuffer:sampleBuffer];
    dispatch_async(dispatch_get_main_queue(), ^{
    //< Add your code here that uses the image >
        [self.imageView setImage:image];
        [self.view setNeedsDisplay];
    }
}

Answer 3

这是一个swift版本的imageFromSampleBuffer函数：

func imageFromSampleBuffer(sampleBuffer:CMSampleBuffer!) -> UIImage {
    let imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer)!
    CVPixelBufferLockBaseAddress(imageBuffer, 0)

    let baseAddress = CVPixelBufferGetBaseAddress(imageBuffer)
    let bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer)
    let width = CVPixelBufferGetWidth(imageBuffer)
    let height = CVPixelBufferGetHeight(imageBuffer)

    let colorSpace = CGColorSpaceCreateDeviceRGB()

    let bitmapInfo:CGBitmapInfo = [.ByteOrder32Little, CGBitmapInfo(rawValue: CGImageAlphaInfo.PremultipliedFirst.rawValue)]
    let context = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace, bitmapInfo.rawValue)

    let quartzImage = CGBitmapContextCreateImage(context)
    CVPixelBufferUnlockBaseAddress(imageBuffer, 0)

    let image = UIImage(CGImage: quartzImage!)
    return image
}

以上视频设置为我工作：

videoDataOutput = AVCaptureVideoDataOutput()
videoDataOutput?.videoSettings = [kCVPixelBufferPixelFormatTypeKey:Int(kCVPixelFormatType_32BGRA)]
            videoDataOutput?.setSampleBufferDelegate(self, queue: queue)

ios使用AVFramework捕获图像

3 个答案: