AVCaptureStillImageOutput 从不调用完成处理程序答案

【问题标题】：AVCaptureStillImageOutput never calls completition handlerAVCaptureStillImageOutput 从不调用完成处理程序
【发布时间】：2012-09-08 20:26:03
【问题描述】：

以下代码不起作用。怎么了？

AVCaptureDevice * videoDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
AVCaptureDeviceInput * videoInput = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:nil];
AVCaptureSession * captureSession = [[AVCaptureSession alloc] init];
captureSession.sessionPreset = AVCaptureSessionPresetMedium;
if (![captureSession canAddInput:videoInput])
    NSLog(@"Can't add input");
[captureSession addInput:videoInput];

self.stillImageOutput = [[AVCaptureStillImageOutput alloc] init];
[self.stillImageOutput setOutputSettings:@{AVVideoCodecKey:AVVideoCodecJPEG}];
if (![captureSession canAddOutput:videoInput])
    NSLog(@"Can't add output");
[captureSession addOutput:self.stillImageOutput];

[self.stillImageOutput captureStillImageAsynchronouslyFromConnection:[self.stillImageOutput.connections lastObject]
                                                   completionHandler:^(CMSampleBufferRef imageDataSampleBuffer, NSError *error)
                                                   {
                                                       NSLog(@"!!!");

                                                       if (imageDataSampleBuffer == NULL)
                                                       {
                                                           NSLog(@"%@", error);
                                                           return;
                                                       }

                                                       NSData *imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageDataSampleBuffer];
                                                       UIImage *image = [[UIImage alloc] initWithData:imageData];
                                                       self.imageView.image = image;
                                                   }];

// Creating preview layer
self.previewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:captureSession];
self.previewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
self.previewLayer.frame = self.view.layer.bounds;
[self.view.layer addSublayer:self.previewLayer];

[captureSession startRunning];

AVCaptureVideoPreviewLayer 效果很好，但 AVCaptureStillImageOutput 根本不调用完成处理程序...

【问题讨论】：

标签： ios camera avfoundation video-capture

【解决方案1】：

您需要以一种方法设置和启动会话，然后有一个单独的捕获方法：

/////////////////////////////////////////////////
////
//// Utility to find front camera
////
/////////////////////////////////////////////////
-(AVCaptureDevice *) frontFacingCameraIfAvailable{

    NSArray *videoDevices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
    AVCaptureDevice *captureDevice = nil;

   for (AVCaptureDevice *device in videoDevices){

        if (device.position == AVCaptureDevicePositionFront){

            captureDevice = device;
            break;
        }
    }

    //  couldn't find one on the front, so just get the default video device.
    if (!captureDevice){

        captureDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    }

    return captureDevice;
}

/////////////////////////////////////////////////
////
//// Setup Session, attach Video Preview Layer
//// and Capture Device, start running session
////
/////////////////////////////////////////////////
-(void) setupCaptureSession {
    AVCaptureSession *session = [[AVCaptureSession alloc] init];
    session.sessionPreset = AVCaptureSessionPresetMedium;

    AVCaptureVideoPreviewLayer *captureVideoPreviewLayer = [[AVCaptureVideoPreviewLayer    alloc] initWithSession:session];
    [self.view.layer addSublayer:captureVideoPreviewLayer];

    NSError *error = nil;
    AVCaptureDevice *device = [self frontFacingCameraIfAvailable];
    AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device error:&error];
    if (!input) {
        // Handle the error appropriately.
        NSLog(@"ERROR: trying to open camera: %@", error);
    }
    [session addInput:input];

    self.stillImageOutput = [[AVCaptureStillImageOutput alloc] init];
    NSDictionary *outputSettings = [[NSDictionary alloc] initWithObjectsAndKeys: AVVideoCodecJPEG, AVVideoCodecKey, nil];
    [self.stillImageOutput setOutputSettings:outputSettings];

    [session addOutput:self.stillImageOutput];

    [session startRunning];
}


/////////////////////////////////////////////////
////
//// Method to capture Still Image from 
//// Video Preview Layer
////
/////////////////////////////////////////////////
-(void) captureNow {
    AVCaptureConnection *videoConnection = nil;
    for (AVCaptureConnection *connection in self.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: %@", self.stillImageOutput);
    __weak typeof(self) weakSelf = self;
    [self.stillImageOutput captureStillImageAsynchronouslyFromConnection:videoConnection completionHandler: ^(CMSampleBufferRef imageSampleBuffer, NSError *error) {

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

         [weakSelf displayImage:image];
     }];
}

【讨论】：

“在单独的方法中执行”解决此问题的唯一原因是它具有将 AVCaptureSession 保留在控制器中的副作用。我认为 AVCaptureStillImageOutput 中存在一个错误，使其在自动引用计数模式下无法跟踪其 AVCaptureSession。
啊，好点子。是的 - 我和一位同事试图让它像你上周五尝试的那样工作，但没有运气。我一直到凌晨，发现最好单独初始化 AVCaptureSession。祝你好运！
我正在尝试在 swift 中做同样的事情，但它不起作用.....有没有它不起作用的原因..我有相同的代码....
在我的情况下 stillImageOutput.connections 是 nil 因为我分配了 AVCaptureSession 和 AVCaptureVideoPreviewLayer 两次，所以只需添加检查 session == nil 然后只做 [[AVCaptureStillImageOutput alloc] init] 和所有 StillImageOutput 预设跨度>

【解决方案2】：

这很好用：

- (void)viewDidLoad
{
    [super viewDidLoad];

    AVCaptureDevice * videoDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    AVCaptureDeviceInput * videoInput = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:nil];
    AVCaptureSession * captureSession = [[AVCaptureSession alloc] init];
    captureSession.sessionPreset = AVCaptureSessionPresetMedium;
    [captureSession addInput:videoInput];
    [captureSession addOutput:self.stillImageOutput];
    [captureSession startRunning];

    // Creating preview layer
    self.previewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:captureSession];
    self.previewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
    self.previewLayer.frame = self.view.layer.bounds;
    [self.view.layer insertSublayer:self.previewLayer atIndex:0];
}

- (void)timerFired:(NSTimer *)timer
{
    [self.stillImageOutput captureStillImageAsynchronouslyFromConnection:[self.stillImageOutput.connections lastObject]
                                                       completionHandler:^(CMSampleBufferRef imageDataSampleBuffer, NSError *error)
                                                       {
                                                           NSLog(@"!!!");

                                                           if (imageDataSampleBuffer == NULL)
                                                               NSLog(@"%@", error);

                                                           NSData * imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageDataSampleBuffer];
                                                           UIImage * image = [[UIImage alloc] initWithData:imageData];
                                                           self.imageView.image = image;
                                                       }];
}

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];

    [NSTimer scheduledTimerWithTimeInterval:0.5 target:self selector:@selector(timerFired:) userInfo:nil repeats:YES];
}

【讨论】：