我想从AVCaptureSession的实时供稿中提取帧，我正在使用Apple的AVCam作为测试用例。这是AVCam的链接:
https://developer.apple.com/library/ios/samplecode/AVCam/Introduction/Intro.html
我发现未调用captureOutput:didOutputSampleBuffer:fromConnection，我想知道为什么或做错了什么。
这是我所做的:
(1)我将AVCamViewController委托(delegate)给
@interface AVCamViewController () <AVCaptureFileOutputRecordingDelegate, AVCaptureVideoDataOutputSampleBufferDelegate>
(2)我创建了一个
AVCaptureVideoDataOutput对象并将其添加到 session 中AVCaptureVideoDataOutput *videoDataOutput = [[AVCaptureVideoDataOutput alloc] init];
if ([session canAddOutput:videoDataOutput])
{
[session addOutput:videoDataOutput];
}
(3)我添加了委托(delegate)方法并通过记录一个随机字符串进行测试
- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection
{
NSLog(@"I am called");
}
测试应用程序可以工作，但是不调用captureOutput:didOutputSampleBuffer:fromConnection。
(4)我在SO上读到，
AVCaptureSession *session = [[AVCaptureSession alloc] init];中的session变量在viewDidLoad中是本地的，这可能是未调用该委托(delegate)的可能原因，并且我将其设为AVCamViewController类的实例变量，但未调用它。这是我正在测试的viewDidLoad方法(摘自AVCam)，我在方法末尾添加了AVCaptureDataOutput:
- (void)viewDidLoad
{
[super viewDidLoad];
// Create the AVCaptureSession
session = [[AVCaptureSession alloc] init];
[self setSession:session];
// Setup the preview view
[[self previewView] setSession:session];
// Check for device authorization
[self checkDeviceAuthorizationStatus];
// In general it is not safe to mutate an AVCaptureSession or any of its inputs, outputs, or connections from multiple threads at the same time.
// Why not do all of this on the main queue?
// -[AVCaptureSession startRunning] is a blocking call which can take a long time. We dispatch session setup to the sessionQueue so that the main queue isn't blocked (which keeps the UI responsive).
dispatch_queue_t sessionQueue = dispatch_queue_create("session queue", DISPATCH_QUEUE_SERIAL);
[self setSessionQueue:sessionQueue];
dispatch_async(sessionQueue, ^{
[self setBackgroundRecordingID:UIBackgroundTaskInvalid];
NSError *error = nil;
AVCaptureDevice *videoDevice = [AVCamViewController deviceWithMediaType:AVMediaTypeVideo preferringPosition:AVCaptureDevicePositionBack];
AVCaptureDeviceInput *videoDeviceInput = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:&error];
if (error)
{
NSLog(@"%@", error);
}
if ([session canAddInput:videoDeviceInput])
{
[session addInput:videoDeviceInput];
[self setVideoDeviceInput:videoDeviceInput];
dispatch_async(dispatch_get_main_queue(), ^{
// Why are we dispatching this to the main queue?
// Because AVCaptureVideoPreviewLayer is the backing layer for AVCamPreviewView and UIView can only be manipulated on main thread.
// Note: As an exception to the above rule, it is not necessary to serialize video orientation changes on the AVCaptureVideoPreviewLayer’s connection with other session manipulation.
[[(AVCaptureVideoPreviewLayer *)[[self previewView] layer] connection] setVideoOrientation:(AVCaptureVideoOrientation)[self interfaceOrientation]];
});
}
AVCaptureDevice *audioDevice = [[AVCaptureDevice devicesWithMediaType:AVMediaTypeAudio] firstObject];
AVCaptureDeviceInput *audioDeviceInput = [AVCaptureDeviceInput deviceInputWithDevice:audioDevice error:&error];
if (error)
{
NSLog(@"%@", error);
}
if ([session canAddInput:audioDeviceInput])
{
[session addInput:audioDeviceInput];
}
AVCaptureMovieFileOutput *movieFileOutput = [[AVCaptureMovieFileOutput alloc] init];
if ([session canAddOutput:movieFileOutput])
{
[session addOutput:movieFileOutput];
AVCaptureConnection *connection = [movieFileOutput connectionWithMediaType:AVMediaTypeVideo];
if ([connection isVideoStabilizationSupported])
[connection setEnablesVideoStabilizationWhenAvailable:YES];
[self setMovieFileOutput:movieFileOutput];
}
AVCaptureStillImageOutput *stillImageOutput = [[AVCaptureStillImageOutput alloc] init];
if ([session canAddOutput:stillImageOutput])
{
[stillImageOutput setOutputSettings:@{AVVideoCodecKey : AVVideoCodecJPEG}];
[session addOutput:stillImageOutput];
[self setStillImageOutput:stillImageOutput];
}
AVCaptureVideoDataOutput *videoDataOutput = [[AVCaptureVideoDataOutput alloc] init];
[videoDataOutput setSampleBufferDelegate:self queue:sessionQueue];
if ([session canAddOutput:videoDataOutput])
{
NSLog(@"Yes I can add it");
[session addOutput:videoDataOutput];
}
});
}
- (void)viewWillAppear:(BOOL)animated
{
dispatch_async([self sessionQueue], ^{
[self addObserver:self forKeyPath:@"sessionRunningAndDeviceAuthorized" options:(NSKeyValueObservingOptionOld | NSKeyValueObservingOptionNew) context:SessionRunningAndDeviceAuthorizedContext];
[self addObserver:self forKeyPath:@"stillImageOutput.capturingStillImage" options:(NSKeyValueObservingOptionOld | NSKeyValueObservingOptionNew) context:CapturingStillImageContext];
[self addObserver:self forKeyPath:@"movieFileOutput.recording" options:(NSKeyValueObservingOptionOld | NSKeyValueObservingOptionNew) context:RecordingContext];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(subjectAreaDidChange:) name:AVCaptureDeviceSubjectAreaDidChangeNotification object:[[self videoDeviceInput] device]];
__weak AVCamViewController *weakSelf = self;
[self setRuntimeErrorHandlingObserver:[[NSNotificationCenter defaultCenter] addObserverForName:AVCaptureSessionRuntimeErrorNotification object:[self session] queue:nil usingBlock:^(NSNotification *note) {
AVCamViewController *strongSelf = weakSelf;
dispatch_async([strongSelf sessionQueue], ^{
// Manually restarting the session since it must have been stopped due to an error.
[[strongSelf session] startRunning];
[[strongSelf recordButton] setTitle:NSLocalizedString(@"Record", @"Recording button record title") forState:UIControlStateNormal];
});
}]];
[[self session] startRunning];
});
}
有人可以告诉我原因以及如何解决的建议吗？
最佳答案
我已经做了很多实验，我想我可能已经找到了答案。我有类似但不同的代码，它们是从头开始编写的，而不是从Apple的示例(现在有点旧)中复制的。
我认为这是部分...
AVCaptureMovieFileOutput *movieFileOutput = [[AVCaptureMovieFileOutput alloc] init];
if ([session canAddOutput:movieFileOutput])
{
[session addOutput:movieFileOutput];
AVCaptureConnection *connection = [movieFileOutput connectionWithMediaType:AVMediaTypeVideo];
if ([connection isVideoStabilizationSupported])
[connection setEnablesVideoStabilizationWhenAvailable:YES];
[self setMovieFileOutput:movieFileOutput];
}
根据我的实验，这就是导致您出现问题的原因。在我的代码中，当它存在时，
captureOutput:didOutputSampleBuffer:fromConnection不被调用。我认为视频系统EITHER为您提供了一系列样本缓冲区，或者将压缩的，优化的电影文件记录到磁盘上，而不是同时记录在磁盘上。 (至少在iOS上。)我认为这是有道理的/不足为奇，但是我还没有在任何地方看到它的记录!另外，有一点我似乎在打开麦克风时遇到错误和/或没有发生缓冲区回调。再次未记录，这些是错误-11800(未知错误)。但是我不能总是重现这一点。