UIImage von AVCaptureVideoPreviewLayer

Question

Ich versuche, ein Standbild aus einem Videofeed (im Grunde eine Pause oder "Schnappschuss" -Funktion) zu greifen. Mein Projekt wird unter Verwendung von Benjamin Loulier's template eingerichtet. Mein Problem ist, dass, obwohl ich Farbvideo auf dem Bildschirm über die prevLayer (ein AVCaptureVideoPreviewLayer) anzeigen, habe ich die Videoeinstellungen auf Graustufen festgelegt, so kann ich kein UIImage von customLayer (ein regulärer CALayer).

Ich habe versucht, diese Funktion here gegeben verwenden, aber dies aus irgendeinem dummen Grund für AVCaptureVideoPreviewLayer funktioniert nicht (zeigt sich klar/transparent). Kennt jemand eine Methode, um den Inhalt eines AVCaptureVideoPreviewLayer als UIImage zu speichern?

Answer 1

Ok das ist meine Antwort, mit freundlicher Genehmigung von https://developer.apple.com/library/ios/#qa/qa1702/_index.html

Eine Anmerkung. minFrameDuration ist seit iOS 5.0 veraltet. Nicht sicher über den Grund oder wenn es einen Ersatz gibt.

#import <AVFoundation/AVFoundation.h> 

// 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) { 
     // Handling the error appropriately. 
    } 
    [session addInput:input]; 

    // Create a VideoDataOutput and add it to the session 
    AVCaptureVideoDataOutput *output = [[[AVCaptureVideoDataOutput alloc] init] autorelease]; 
    [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, 15); 

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

    < Add your code here that uses the image > 

} 

// Create a UIImage from sample buffer data 
- (UIImage *) imageFromSampleBuffer:(CMSampleBufferRef) sampleBuffer 
{ 
    // 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); 
}