Question

当我创建第二个AVCaptureSession时，自动对焦无法在第一个AVCaptureSession上运行。要创建的第二个会话是自动对焦工作的会话，第一个创建的会话不会自动对焦。

我希望任何一个会话都可以在另一个会话停止后自动对焦，就像两个会话的自动白平衡和自动曝光工作一样。如果您使用下面的示例代码观察日志窗口，您可以看到通过的键值观察消息;但是在最高会话运行时从不改变焦点消息。

旁注：不幸的是我在我使用的第三方库中有一个错误，这使我无法简单地重新创建会话，因为我在它们之间切换（它正在泄漏其AVCaptureSessions，最终导致应用程序被杀死）。完整的故事是这个库正在为我创建一个捕获会话，它有一个公共API来启动和停止会话，我希望创建另一个会话。下面的代码演示了问题，但没有使用第三方库。

我创建了一个测试应用程序，其中包含下面列出的代码和一个有两个视图的XIB文件，一个在另一个之上，另一个按钮连接到switchSessions方法，用于演示该问题。

这可能与此处描述的问题有关， Focus (Autofocus) not working in camera (AVFoundation AVCaptureSession)，虽然没有提到两个捕获会议。

标题文件：

#import <UIKit/UIKit.h>

@class AVCaptureSession;
@class AVCaptureStillImageOutput;
@class AVCaptureVideoPreviewLayer;
@class AVCaptureDevice;
@class AVCaptureDeviceInput;

@interface AVCaptureSessionFocusBugViewController : UIViewController {

    IBOutlet UIView *_topView;
    IBOutlet UIView *_bottomView;

    AVCaptureDevice *_device;

    AVCaptureSession *_topSession;

    AVCaptureStillImageOutput *_outputTopSession;
    AVCaptureVideoPreviewLayer *_previewLayerTopSession;
    AVCaptureDeviceInput *_inputTopSession;

    AVCaptureSession *_bottomSession;

    AVCaptureStillImageOutput *_outputBottomSession;
    AVCaptureVideoPreviewLayer *_previewLayerBottomSession;
    AVCaptureDeviceInput *_inputBottomSession;
}

- (IBAction)switchSessions:(id)sender;

@end

实施档案：

#import "AVCaptureSessionFocusBugViewController.h"
#import <AVFoundation/AVFoundation.h>

@interface AVCaptureSessionFocusBugViewController ()

- (void)setupCaptureSession:(AVCaptureSession **)session
                     output:(AVCaptureStillImageOutput **)output
               previewLayer:(AVCaptureVideoPreviewLayer **)previewLayer
                      input:(AVCaptureDeviceInput **)input
                       view:(UIView *)view;

- (void)tearDownSession:(AVCaptureSession **)session
                 output:(AVCaptureStillImageOutput **)output
           previewLayer:(AVCaptureVideoPreviewLayer **)previewLayer
                  input:(AVCaptureDeviceInput **)input
                   view:(UIView *)view;

@end

@implementation AVCaptureSessionFocusBugViewController

- (IBAction)switchSessions:(id)sender
{
    if ([_topSession isRunning]) {
        [_topSession stopRunning];
        [_bottomSession startRunning];
        NSLog(@"Bottom session now running.");
    }
    else {
        [_bottomSession stopRunning];
        [_topSession startRunning];
        NSLog(@"Top session now running.");
    }
}

- (void)observeValueForKeyPath:(NSString *)keyPath 
                      ofObject:(id)object 
                        change:(NSDictionary *)change 
                       context:(void *)context
{
    NSLog(@"Observed value for key at key path %@.", keyPath);
    // Enable to confirm that the focusMode is set correctly.
    //NSLog(@"Autofocus for the device is set to %d.", [_device focusMode]);
}

- (void)viewDidLoad {
    [super viewDidLoad];

    _device = [[AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo] retain];

    [self setupCaptureSession:&_topSession 
                       output:&_outputTopSession
                 previewLayer:&_previewLayerTopSession
                        input:&_inputTopSession
                         view:_topView];

    [self setupCaptureSession:&_bottomSession 
                       output:&_outputBottomSession
                 previewLayer:&_previewLayerBottomSession
                        input:&_inputBottomSession
                         view:_bottomView];

    // NB: We only need to observe one device, since the top and bottom sessions use the same device.
    [_device addObserver:self forKeyPath:@"adjustingFocus" options:NSKeyValueObservingOptionNew context:nil];
    [_device addObserver:self forKeyPath:@"adjustingExposure" options:NSKeyValueObservingOptionNew context:nil];
    [_device addObserver:self forKeyPath:@"adjustingWhiteBalance" options:NSKeyValueObservingOptionNew context:nil];

    [_topSession startRunning];
    NSLog(@"Starting top session.");
}


- (void)setupCaptureSession:(AVCaptureSession **)session
                     output:(AVCaptureStillImageOutput **)output
               previewLayer:(AVCaptureVideoPreviewLayer **)previewLayer
                      input:(AVCaptureDeviceInput **)input
                       view:(UIView *)view
{    
    *session = [[AVCaptureSession alloc] init];

    // Create the preview layer.
    *previewLayer = [[AVCaptureVideoPreviewLayer layerWithSession:*session] retain];

    [*previewLayer setVideoGravity:AVLayerVideoGravityResizeAspectFill];

    [*previewLayer setFrame:[view bounds]];

    [[view layer] addSublayer:*previewLayer];

    // Configure the inputs and outputs.
    [*session setSessionPreset:AVCaptureSessionPresetMedium];

    NSError *error = nil;

    *input = [[AVCaptureDeviceInput deviceInputWithDevice:_device error:&error] retain];

    if (!*input) {
        NSLog(@"Error creating input device:%@", [error localizedDescription]);
        return;
    }

    [*session addInput:*input];

    *output = [[AVCaptureStillImageOutput alloc] init];

    [*session addOutput:*output];

    NSDictionary *outputSettings = [[NSDictionary alloc] initWithObjectsAndKeys:AVVideoCodecJPEG, AVVideoCodecKey, nil];

    [*output setOutputSettings:outputSettings];

    [outputSettings release];
}

- (void)viewDidUnload {
    [_topView release];
    _topView = nil;

    [_bottomView release];
    _bottomView = nil;

    [_device release];
    _device = nil;

    [self tearDownSession:&_topSession
                   output:&_outputTopSession
             previewLayer:&_previewLayerTopSession
                    input:&_inputTopSession
                     view:_topView];

    [self tearDownSession:&_bottomSession 
                       output:&_outputBottomSession
                 previewLayer:&_previewLayerBottomSession
                        input:&_inputBottomSession
                         view:_bottomView];
}

- (void)tearDownSession:(AVCaptureSession **)session
                 output:(AVCaptureStillImageOutput **)output
           previewLayer:(AVCaptureVideoPreviewLayer **)previewLayer
                  input:(AVCaptureDeviceInput **)input
                   view:(UIView *)view
{
    if ([*session isRunning]) {
        [*session stopRunning];
    }

    [*session removeOutput:*output];

    [*output release];
    *output = nil;

    [*session removeInput:*input];

    [*input release];
    *input = nil;

    [*previewLayer removeFromSuperlayer];

    [*previewLayer release];
    *previewLayer = nil;

    [*session release];
    *session = nil;
}

@end

Answer 1

Apple技术支持已确认不支持创建两个同时捕获会话。你必须拆掉一个，然后创建另一个。

如何在不重新创建会话的情况下让自动对焦在第二个AVCaptureSession中工作？

1 个答案: