Question

我正在学习AVCaptureSession以及如何使用其委托方法捕获多个图像

- (void)captureOutput:(AVCaptureOutput *)captureOutput 
     didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer 
     fromConnection:(AVCaptureConnection *)connection

我的目标是以每秒预定义的速率捕获1个或多个图像。例如，每1秒1或2个图像。所以我设置了

 AVCaptureVideoDataOutput *captureOutput = [[AVCaptureVideoDataOutput alloc] init];
 captureOutput.alwaysDiscardsLateVideoFrames = YES; 
 captureOutput.minFrameDuration = CMTimeMake(1, 1);

启动[self.captureSession startRunning];时，我的日志文件显示委托每秒被调用20次。它来自何处以及如何以我预期的间隔捕获图像？

Answer 1

您可以使用下面给出的功能，如果您想以特定间隔捕获，则设置计时器并再次调用该功能。

-(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(@"Attachments: %@", exifAttachments);
        }
        else
        { 
            NSLog(@"No attachments found.");
        }

        NSData *imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageSampleBuffer];
        UIImage *image = [[UIImage alloc] initWithData:imageData];
        [[self vImage] setImage:image];

    }];
}

有关详情，请参阅iOS4: Take photos with live video preview using AVFoundation。

Answer 2

我挣扎了一段时间的东西是拍摄照片时的大幅延迟（约5秒），并试图用拍摄的图像设置UIImage。在

 - (void)captureOutput:(AVCaptureOutput *)captureOutput 
 didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer 
 fromConnection:(AVCaptureConnection *)connection

方法，你不能使用[self.image setImage:img]之类的常规函数来处理链接到UI的东西，你必须在主线程上运行它们，如下所示：

 [self.image performSelectorOnMainThread:@selector(setImage:) withObject:img waitUntilDone:TRUE];

希望这有助于某人

从AVCaptureSession捕获图像

2 个答案: