AVCaptureSession拍照时如何设置扫描速率

转载自：http://stackoverflow.com/questions/8264749/capturing-images-from-avcapturesession

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I am learning about AVCaptureSession and how to capture multiple images with its delegate method - (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection My goal is to capture 1 or many images with a predefined rate per second. For example, 1 or 2 images per 1 second. So I set AVCaptureVideoDataOutput *captureOutput = [[AVCaptureVideoDataOutput alloc] init]; captureOutput.alwaysDiscardsLateVideoFrames = YES; captureOutput.minFrameDuration = CMTimeMake(1, 1); When [self.captureSession startRunning]; is started my log file shows delegate is being called 20 times a second. Where is it coming from and how to capture images with my intended intervals? iphone  objective-c  uiimageview  calayer  avcapturesession share | improve this question edited Nov 25 '11 at 5:25 Aadhira 11.8k 1 18 39 asked  Nov 25 '11 at 4:13 Vad 648 1 9 28

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You can use the function given below and if you want to capture at specific intervals, then set a timer and call that function again. -(IBAction) captureNow { AVCaptureConnection *videoConnection = nil; for (AVCaptureConnection *connection in stillImageOutput.connections) { for (AVCaptureInputPort *port in [connection inputPorts]) { if ([[port mediaType] isEqual:AVMediaTypeVideo] ) { videoConnection = connection; break; } } if (videoConnection) { break; } } NSLog(@"about to request a capture from: %@", stillImageOutput); [stillImageOutput captureStillImageAsynchronouslyFromConnection:videoConnection completionHandler: ^(CMSampleBufferRef imageSampleBuffer, NSError *error) { CFDictionaryRef exifAttachments = CMGetAttachment( imageSampleBuffer, kCGImagePropertyExifDictionary, NULL); if (exifAttachments) { // Do something with the attachments. NSLog(@"attachements: %@", exifAttachments); } else NSLog(@"no attachments"); NSData *imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageSampleBuffer]; UIImage *image = [[UIImage alloc] initWithData:imageData]; self.vImage.image = image; }]; } For more reference you can see iOS4: Take photos with live video preview using AVFoundation. share | improve this answer edited Apr 24 at 7:24 David Rönnqvist 16.8k 5 34 63 answered  Nov 25 '11 at 5:28 Ajeet Pratap Maurya 2,464 1 9 27

Very helpful! Thanks a lot. –   Vad  Nov 25 '11 at 18:43 add comment

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Something that I struggled with for a while was a massive delay (~5 sec) when taking a picture, and trying to set a UIImage with the captured image. in the - (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection method, you cant use normal functions such as [self.image setImage:img] for things that are linked to the UI, you have to run them on the main thread like so: [self.image performSelectorOnMainThread:@selector(setImage:) withObject:img waitUntilDone:TRUE]; Hope this helps someone