AVCaptureSession拍照时如何设置扫描速率

最新推荐文章于 2021-01-16 09:43:42 发布

转载最新推荐文章于 2021-01-16 09:43:42 发布 · 3.7k 阅读

本文探讨了如何使用AVCaptureSession及其代理方法捕获单张或多张图片，并介绍了如何通过设置来实现每秒捕获一张或几张图片的目标。文中提供了一个示例函数，用于按特定间隔捕获图像。

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?

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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2 Answers

active oldest votes

up vote 4 down vote accepted

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.

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

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up vote 0 down vote

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