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如何正确释放AVCaptureSession

avfoundation camera ios multithreading iphone

Codo · 技术社区 · 14 年前

我正在使用AVFoundation类从摄像机捕获实时视频流并处理视频样本。这个很好用。但是,一旦完成,我就很难正确地释放AVFoundation实例(捕获会话、预览层、输入和输出)。

当我不再需要会话和所有相关对象时,我会停止捕获会话并释放它。这在大多数情况下都有效。但是,有时应用程序会因错误而崩溃 EXEC_BAD_ACCESS

Apple文档提到了这个问题:停止捕获会话是一个异步操作。也就是说:它不会立即发生。特别地,第二线程继续处理视频样本并访问不同的实例,如捕获会话或输入和输出设备。

那么,如何正确地释放 AVCaptureSession 以及所有相关实例?是否有通知可靠地告诉我 AVCaptureSession会话 完成了吗?

这是我的密码:

AVCaptureSession* session;
AVCaptureVideoPreviewLayer* previewLayer;
UIView* view;

实例设置:

AVCaptureDevice* camera = [AVCaptureDevice defaultDeviceWithMediaType: AVMediaTypeVideo];
session = [[AVCaptureSession alloc] init];

AVCaptureDeviceInput* input = [AVCaptureDeviceInput deviceInputWithDevice: camera error: &error];
[session addInput: input];
AVCaptureVideoDataOutput* output = [[[AVCaptureVideoDataOutput alloc] init] autorelease];
[session addOutput: output];

dispatch_queue_t queue = dispatch_queue_create("augm_reality", NULL);
[output setSampleBufferDelegate: self queue: queue];
dispatch_release(queue);

previewLayer = [[AVCaptureVideoPreviewLayer layerWithSession: session] retain];
previewLayer.frame = view.bounds;
[view.layer addSublayer: previewLayer];

[session startRunning];

清理:

[previewLayer removeFromSuperlayer];
[previewLayer release];
[session stopRunning];
[session release];

7 回复 | 直到 4 年前

Community CDub 13 年前

这是迄今为止我找到的最好的解决办法。基本思想是使用调度队列的终结器。当分派队列退出时,我们可以确定在处理样本缓冲区的第二个线程中不会有任何操作。

static void capture_cleanup(void* p)
{
    AugmReality* ar = (AugmReality *)p; // cast to original context instance
    [ar release];  // releases capture session if dealloc is called
}

...

dispatch_queue_t queue = dispatch_queue_create("augm_reality", NULL);
dispatch_set_context(queue, self);
dispatch_set_finalizer_f(queue, capture_cleanup);
[output setSampleBufferDelegate: self queue: queue];
dispatch_release(queue);
[self retain];

...

不幸的是,我现在必须明确停止捕捉。否则释放我的实例不会释放它,因为第二个线程现在也会增加和减少计数器。

Codo 14 年前

我在苹果开发者论坛上发布了一个非常类似的问题,得到了一位苹果员工的回答。他说这是一个已知的问题:

iOS 4.0-4.1已修复,将在将来的更新中出现。为了停止AVCaptureSession,例如,在处理会话和数据输出。

dispatch_after(
    dispatch_time(0, 500000000),
    dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), // or main queue, or your own
    ^{
        // Do your work here.
        [session release];
        // etc.
    }
);

我仍然更喜欢使用dispatch queue finalizer的方法,因为这段代码只是猜测第二个线程何时完成。

kiranpradeep 9 年前

根据当前苹果文件( 1 ) [AVCaptureSession stopRunning]

VLegakis 14 年前

解决了的! 可能是初始化会话时的一系列动作。这个对我有用:

NSError *error = nil;

if(session)
    [session release];

// Create the session
session = [[AVCaptureSession alloc] init];


// Configure the session to produce lower resolution video frames, if your 
// processing algorithm can cope. We'll specify medium quality for the
// chosen device.
session.sessionPreset = AVCaptureSessionPresetMedium;

// Find a suitable AVCaptureDevice
AVCaptureDevice *device = [AVCaptureDevice
                           defaultDeviceWithMediaType:AVMediaTypeVideo];

// Create a device input with the device and add it to the session.
AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device 
                                                                    error:&error];
if (!input) {
    // Handling the error appropriately.
}
[session addInput:input];

// Create a VideoDataOutput and add it to the session
AVCaptureVideoDataOutput *output = [[[AVCaptureVideoDataOutput alloc] init] autorelease];
[session addOutput:output];


// Configure your output.
dispatch_queue_t queue = dispatch_queue_create("myQueue", NULL);
[output setSampleBufferDelegate:self queue:queue];
dispatch_release(queue);

// Specify the pixel format
output.videoSettings = 
[NSDictionary dictionaryWithObject:
 [NSNumber numberWithInt:kCVPixelFormatType_32BGRA] 
                            forKey:(id)kCVPixelBufferPixelFormatTypeKey];

// If you wish to cap the frame rate to a known value, such as 15 fps, set 
// minFrameDuration.
output.minFrameDuration = CMTimeMake(1, 15);

previewLayer = [AVCaptureVideoPreviewLayer layerWithSession:session];
[delegate layerArrived:previewLayer];

NSNotificationCenter *notify =
[NSNotificationCenter defaultCenter];
[notify addObserver: self
            selector: @selector(onVideoError:)
            name: AVCaptureSessionRuntimeErrorNotification
            object: session];
[notify addObserver: self
            selector: @selector(onVideoStart:)
            name: AVCaptureSessionDidStartRunningNotification
            object: session];
[notify addObserver: self
            selector: @selector(onVideoStop:)
            name: AVCaptureSessionDidStopRunningNotification
            object: session];
[notify addObserver: self
            selector: @selector(onVideoStop:)
            name: AVCaptureSessionWasInterruptedNotification
            object: session];
[notify addObserver: self
            selector: @selector(onVideoStart:)
            name: AVCaptureSessionInterruptionEndedNotification
            object: session];

// Start the session running to start the flow of data
[session startRunning];

Mahyar 13 年前

使用队列终结器,可以为每个队列使用dispatch\信号量,然后在完成后继续执行清理例程。

#define GCD_TIME(delayInSeconds) dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC)

static void vQueueCleanup(void* context) {
  VideoRecordingViewController *vc = (VideoRecordingViewController*)context;
  if (vc.vSema) dispatch_semaphore_signal(vc.vSema);
}

static void aQueueCleanup(void* context) {
  VideoRecordingViewController *vc = (VideoRecordingViewController*)context;
  if (vc.aSema) dispatch_semaphore_signal(vc.aSema);
}

//In your cleanup method:
vSema = dispatch_semaphore_create(0);
aSema = dispatch_semaphore_create(0);
self.avSession = nil;
if (vSema) dispatch_semaphore_wait(vSema, GCD_TIME(0.5));
if (aSema) dispatch_semaphore_wait(aSema, GCD_TIME(0.5));
[self.navigationController popViewControllerAnimated:YES];

请记住,必须将AVCaptureVideoDataOutput/AVCaptureAudioDataOutput对象示例缓冲区委托设置为nil,否则它们永远不会释放关联的队列,因此在释放AVCaptureSession时永远不会调用终结器。

[avs removeOutput:vOut];
[vOut setSampleBufferDelegate:nil queue:NULL];

souvickcse 11 年前

 -(void)deallocSession
{
[captureVideoPreviewLayer removeFromSuperlayer];
for(AVCaptureInput *input1 in session.inputs) {
    [session removeInput:input1];
}

for(AVCaptureOutput *output1 in session.outputs) {
    [session removeOutput:output1];
}
[session stopRunning];
session=nil;
outputSettings=nil;
device=nil;
input=nil;
captureVideoPreviewLayer=nil;
stillImageOutput=nil;
self.vImagePreview=nil;

}

在弹出和推送任何其他视图之前,我调用了这个函数。它解决了我的低内存警告问题。

VLegakis 14 年前

NSNotificationCenter *notify =
[NSNotificationCenter defaultCenter];
[notify addObserver: self
            selector: @selector(onVideoError:)
            name: AVCaptureSessionRuntimeErrorNotification
            object: session];
[notify addObserver: self
            selector: @selector(onVideoStart:)
            name: AVCaptureSessionDidStartRunningNotification
            object: session];
[notify addObserver: self
            selector: @selector(onVideoStop:)
            name: AVCaptureSessionDidStopRunningNotification
            object: session];
[notify addObserver: self
            selector: @selector(onVideoStop:)
            name: AVCaptureSessionWasInterruptedNotification
            object: session];
[notify addObserver: self
            selector: @selector(onVideoStart:)
            name: AVCaptureSessionInterruptionEndedNotification
            object: session];

AVCaptureInput* input = [session.inputs objectAtIndex:0];
[session removeInput:input];
AVCaptureVideoDataOutput* output = (AVCaptureVideoDataOutput*)[session.outputs objectAtIndex:0];
[session removeOutput:output];

它的工作,但请让我知道,如果你看到任何把戏。我更喜欢异步使用它。

谢谢