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我正在尝试使用AVFoundation以下代码在框架中使用 iOS7 QR 读取功能：

-(void)setupCaptureSession_iOS7 {
    self.session = [[AVCaptureSession alloc] init];
    AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    NSError *error = nil;

    AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device
                                                                        error:&error];
    if (!input)
    {
        NSLog(@"Error: %@", error);
        return;
    }

    [session addInput:input];

    //Turn on point autofocus for middle of view
    [device lockForConfiguration:&error];
    CGPoint point = CGPointMake(0.5,0.5);
    [device setFocusPointOfInterest:point];
    [device setFocusMode:AVCaptureFocusModeContinuousAutoFocus];
    [device unlockForConfiguration];

    //Add the metadata output device
    AVCaptureMetadataOutput *output = [[AVCaptureMetadataOutput alloc] init];
    [output setMetadataObjectsDelegate:self queue:dispatch_get_main_queue()];
    [session addOutput:output];

    NSLog(@"%lu",(unsigned long)output.availableMetadataObjectTypes.count);
    for (NSString *s in output.availableMetadataObjectTypes)
        NSLog(@"%@",s);

    //You should check here to see if the session supports these types, if they aren't support you'll get an exception
    output.metadataObjectTypes = @[AVMetadataObjectTypeEAN13Code, AVMetadataObjectTypeEAN8Code, AVMetadataObjectTypeUPCECode];
    output.rectOfInterest = CGRectMake(0, 0, 320, 480);

    [session startRunning];

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

}

这段代码显然还没有将帧渲染到屏幕上。AVCaptureVideoPreviewLayer这是因为，我需要将帧显示为 a UIImage（这是因为我想在视图上多次显示帧），而不是使用类来显示预览。

如果我AVCaptureVideoDataOutput用作输出，我可以通过从captureOutput:didOutputSampleBuffer:fromConnection:回调中获取帧来导出它们。AVCaptureMetadataOutput但是当用作输出时，我找不到调用 get frameBuffer 的等效方法。

有谁知道如何做到这一点？

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