1. 媒体捕捉的类
AVFoundation的照片和视频捕捉功能是它的强项.先看一下其中捕捉相关的类.
找到唯一比较清楚的图.png
-
捕捉会话 AVCaptureSession:
AVCaptureSession相当于一个虚拟的插座,连接了输入和输出资源.它管理着从物理设备(摄像头和麦克风)得到的数据流,然后输出到其他地方.
可以额外配置一个会话预设值,用来控制捕捉数据的格式和质量,默认是AVCaptureSessionPresetHigh。 -
捕捉设备 AVCaptureDevice:
AVCaptureDevice为物理设备定义一个接口和大量控制方法,例如对焦、曝光、白平衡和闪光等。 -
捕捉设备输入 AVCaptureDeviceInput:
在使用AVCaptureDevice进行处理前,需要将它封装到AVCaptureDeviceInput实例中.因为一个捕捉设备不能直接添加到AVCaptureSession中; 如下:
NSError *error;
AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:&error];
-
捕捉的输出 AVCaptureOutput:
AVCaptureOutput有许多扩展类,它本身只是一个抽象基类,用于为从Session得到的数据寻找输出目的地. 看上面结构图就可以看出各扩展类功能方向, 这里单独说一下,AVCaptureAudioDataOutput和AVCaptureVideoDataOutput可以直接访问硬件扑捉到的数字样本,可以用于音视频流进行实施处理. -
捕捉连接 AVCaptureConnection
这个类其实就是上图中连接不同组件的连接箭头所表示. 对这些连接的访问可以让开发者对信号流就行底层控制,比如禁用某些特定的连接,或者音频连接中限制单独的音频轨道. -
捕捉预览 AVCaptureVideoPreviewLayer
这个类不在上图中, 它是对捕捉视频数据进行实时预览.在视频角色中类似于AVPlayerLayer
捕捉会话应用流程:
- 第一步:配置会话
- (BOOL)setupSession:(NSError **)error {
// 1. 创建捕捉会话
self.captureSession = [[AVCaptureSession alloc] init];
self.captureSession.sessionPreset = AVCaptureSessionPresetHigh;
//2. 根据要生成的媒体类型获取捕捉设备,并添加到Session上.
AVCaptureDevice *videoDevice =
[AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
// 在把此捕捉设备添加到AVCaptureSession之前,先封装成一个input对象.
AVCaptureDeviceInput *videoInput =
[AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:error];
if (videoInput) {
if ([self.captureSession canAddInput:videoInput]) { // 测试是否可以add
[self.captureSession addInput:videoInput];
self.activeVideoInput = videoInput;
}
} else {
return NO;
}
/*// 如果要获取音频捕捉部分
AVCaptureDevice *audioDevice =
[AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio];
AVCaptureDeviceInput *audioInput =
[AVCaptureDeviceInput deviceInputWithDevice:audioDevice error:error];
if (audioInput) {
if ([self.captureSession canAddInput:audioInput]) {
[self.captureSession addInput:audioInput];
}
} else {
return NO;
}
*/
//3. 设置捕捉会话的输出部分
// image输出
self.imageOutput = [[AVCaptureStillImageOutput alloc] init];
self.imageOutput.outputSettings = @{AVVideoCodecKey : AVVideoCodecJPEG};
if ([self.captureSession canAddOutput:self.imageOutput]) {
[self.captureSession addOutput:self.imageOutput];
}
// movie输出
self.movieOutput = [[AVCaptureMovieFileOutput alloc] init];
if ([self.captureSession canAddOutput:self.movieOutput]) {
[self.captureSession addOutput:self.movieOutput];
}
return YES;
}
- 第二: 启动和停止会话
- (void)startSession {
if (![self.captureSession isRunning]) {
dispatch_async([self globalQueue], ^{
[self.captureSession startRunning];
});
}
}
- (void)stopSession {
if ([self.captureSession isRunning]) {
dispatch_async([self globalQueue], ^{
[self.captureSession stopRunning];
});
}
}
// 开始和停止会话都是同步耗时操作,所以采用异步执行.
- (dispatch_queue_t)globalQueue {
return dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
}
iOS 8之后使用硬件设备都需要用户给予权限,使用前都要判断下. 例如:
AVAuthorizationStatus authStatus = [AVCaptureDevice authorizationStatusForMediaType:AVMediaTypeVideo];
if(authStatus == AVAuthorizationStatusRestricted || authStatus == AVAuthorizationStatusDenied) {
NSLog(@"相机权限受限!");
}
2. 细节部分.
2.1 捕捉设备的修改与配置
- 获取摄像头,切换摄像头.
// 当前捕捉会话对应的摄像头.
- (AVCaptureDevice *)activeCamera {
return self.activeVideoInput.device;
}
// 当前未激活的摄像头
- (AVCaptureDevice *)inactiveCamera {
AVCaptureDevice *device = nil;
if (self.cameraCount > 1) {
if ([self activeCamera].position == AVCaptureDevicePositionBack) {
device = [self cameraWithPosition:AVCaptureDevicePositionFront];
} else {
device = [self cameraWithPosition:AVCaptureDevicePositionBack];
}
}
return device;
}
// 切换摄像头
- (BOOL)switchCameras {
if (![self canSwitchCameras]) {
return NO;
}
// 1. 获取当前未使用的摄像头,并为他创建一个新的Input.
NSError *error;
AVCaptureDevice *videoDevice = [self inactiveCamera];
AVCaptureDeviceInput *videoInput =
[AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:&error];
// 2. 用新的Input替换掉正在激活的Input
if (videoInput) {
[self.captureSession beginConfiguration]; // 原子性配置开始.保证线程安全
[self.captureSession removeInput:self.activeVideoInput];
if ([self.captureSession canAddInput:videoInput]) {
[self.captureSession addInput:videoInput];
self.activeVideoInput = videoInput;
} else { // 确保安全,如果新的Input不能添加,继续使用旧的
[self.captureSession addInput:self.activeVideoInput];
}
[self.captureSession commitConfiguration]; // 原子性配置完成
} else { // 错误处理
[self.delegate deviceConfigurationFailedWithError:error];
return NO;
}
return YES;
}
- (BOOL)canSwitchCameras {
return self.cameraCount > 1;
}
- (NSUInteger)cameraCount {
return [[AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo] count];
}
// 获取指定位置的AVCaptureDevice
- (AVCaptureDevice *)cameraWithPosition:(AVCaptureDevicePosition)position {
NSArray *devices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
for (AVCaptureDevice *device in devices) {
if (device.position == position) {
return device;
}
}
return nil;
}
- 调整焦距和曝光
修改AVCaptureDevice配置设备时,一定要先测试修改动作是否被硬件设备支持. 比如前置摄像头不支持对焦操作.尝试一个不被支持的修改动作就会导致程序崩溃. 所以任何修改都要先通过判断一下.
/* 调整对焦 */
- (void)focusAtPoint:(CGPoint)point {
AVCaptureDevice *device = self.activeVideoInput.device;
if (device.isFocusPointOfInterestSupported &&
[device isFocusModeSupported:AVCaptureFocusModeAutoFocus]) { // 判断设备是否支持兴趣点对焦和自动对焦模式.
NSError *error;
if ([device lockForConfiguration:&error]) { // 锁定设备,准备配置修改. 之后修改完释放锁定.
device.focusPointOfInterest = point;
device.focusMode = AVCaptureFocusModeAutoFocus;
[device unlockForConfiguration];
} else {
[self.delegate deviceConfigurationFailedWithError:error];
}
}
}
/*
调整曝光
曝光模式定义了四种方式:
AVCaptureExposureModeLocked 锁定
AVCaptureExposureModeAutoExpose 调整一次并锁定
AVCaptureExposureModeContinuousAutoExposure 一直自动调整
AVCaptureExposureModeCustom
大部分设备是根据环境自动调整, 现在我们做调整曝光度并锁定. 但在iOS中并不支持AVCaptureExposureModeAutoExpose, 所以我们要用其他定义来实现.这个功能
*/
static const NSString *THCameraAdjustingExposureContext;
- (void)exposeAtPoint:(CGPoint)point {
AVCaptureDevice *device = self.activeVideoInput.device;
AVCaptureExposureMode exposureMode =
AVCaptureExposureModeContinuousAutoExposure;
if (device.isExposurePointOfInterestSupported &&
[device isExposureModeSupported:exposureMode]) { // 判断设备是否支持AutoExposure模式
NSError *error;
if ([device lockForConfiguration:&error]) { // 锁定设备,准备配置修改. 之后修改完释放锁定.
device.exposurePointOfInterest = point;
device.exposureMode = exposureMode;
// 判断设备是否支持锁定曝光设置, 如果支持,使用KVO来观察设备"adjustingExposure"属性状态. 然后在曝光调整完成时在该点上锁定曝光.
if ([device isExposureModeSupported:AVCaptureExposureModeLocked]) {
[device addObserver:self
forKeyPath:@"adjustingExposure"
options:NSKeyValueObservingOptionNew
context:&THCameraAdjustingExposureContext];
}
[device unlockForConfiguration];
} else {
[self.delegate deviceConfigurationFailedWithError:error];
}
}
}
- (void)observeValueForKeyPath:(NSString *)keyPath
ofObject:(id)object
change:(NSDictionary *)change
context:(void *)context {
if (context == &THCameraAdjustingExposureContext) {
// 这里通过测试Context是否为&THCameraAdjustingExposureContext指针,来判断监听到的回调是否对应我们期望的变更操作.
AVCaptureDevice *device = (AVCaptureDevice *)object;
if (!device.isAdjustingExposure &&
[device isExposureModeSupported:AVCaptureExposureModeLocked]) {
[object removeObserver:self
forKeyPath:@"adjustingExposure"
context:&THCameraAdjustingExposureContext];
// 回到主队列设置exposureMode
dispatch_async(dispatch_get_main_queue(), ^{
NSError *error;
if ([device lockForConfiguration:&error]) {
device.exposureMode = AVCaptureExposureModeLocked;
[device unlockForConfiguration];
} else {
[self.delegate deviceConfigurationFailedWithError:error];
}
});
}
} else {
[super observeValueForKeyPath:keyPath
ofObject:object
change:change
context:context];
}
}
/* 恢复对焦和曝光设置 */
- (void)resetFocusAndExposureModes {
AVCaptureDevice *device = self.activeVideoInput.device;
AVCaptureExposureMode exposureMode =
AVCaptureExposureModeContinuousAutoExposure;
AVCaptureFocusMode focusMode = AVCaptureFocusModeContinuousAutoFocus;
BOOL canResetFocus = [device isFocusPointOfInterestSupported] &&
[device isFocusModeSupported:focusMode];
BOOL canResetExposure = [device isExposurePointOfInterestSupported] &&
[device isExposureModeSupported:exposureMode];
CGPoint centerPoint = CGPointMake(0.5f, 0.5f); // 创建一个中心扫描点.
NSError *error;
if ([device lockForConfiguration:&error]) {
if (canResetFocus) { // 焦点可以重置
device.focusMode = focusMode;
device.focusPointOfInterest = centerPoint;
}
if (canResetExposure) { // 曝光可以充值
device.exposureMode = exposureMode;
device.exposurePointOfInterest = centerPoint;
}
[device unlockForConfiguration];
} else {
[self.delegate deviceConfigurationFailedWithError:error];
}
}
- 调整闪光灯和手电筒模式(Flash和 Torch 模式)
AVCaptureDevice可以控制摄像头的LED灯,当拍照时是做闪光灯,当拍视频时做手电筒.
- (void)setFlashMode:(AVCaptureFlashMode)flashMode {
AVCaptureDevice *device = self.activeVideoInput.device;
if (device.flashMode != flashMode &&
[device isFlashModeSupported:flashMode]) {
NSError *error;
if ([device lockForConfiguration:&error]) {
device.flashMode = flashMode;
[device unlockForConfiguration];
} else {
[self.delegate deviceConfigurationFailedWithError:error];
}
}
}
- (void)setTorchMode:(AVCaptureTorchMode)torchMode {
AVCaptureDevice *device = self.activeVideoInput.device;
if (device.torchMode != torchMode &&
[device isTorchModeSupported:torchMode]) {
NSError *error;
if ([device lockForConfiguration:&error]) {
device.torchMode = torchMode;
[device unlockForConfiguration];
} else {
[self.delegate deviceConfigurationFailedWithError:error];
}
}
}
3. 基本功能实现-拍照和摄像
- 拍照
上面介绍了基本流程,如果要拍照就是希望捕捉会话的输出Output实例是AVCaptureStillImageOutput类型,这需要在第一步配置会话时添加上去. 而关于接下来具体拍摄方法就定义在AVCaptureStillImageOutput中. 代码如下:
- (void)captureStillImage {
// 获取Output对象当前使用的AVCaptureConnection连接.
// 原始相机只支持垂直方向,所以当设备旋转时,用户界面保持不变.我们希望横向时相应调整图片方向.
AVCaptureConnection *connection =
[self.imageOutput connectionWithMediaType:AVMediaTypeVideo];
// 这里要先确定Connection 是否支持设置视频方向. 然后设置图片方向.
if (connection.isVideoOrientationSupported) {
connection.videoOrientation = [self currentVideoOrientation];
}
id handler = ^(CMSampleBufferRef sampleBuffer, NSError *error) {
if (sampleBuffer != NULL) {
NSData *imageData =
[AVCaptureStillImageOutput
jpegStillImageNSDataRepresentation:sampleBuffer];
// 得到的照片
UIImage *image = [[UIImage alloc] initWithData:imageData];
} else {
NSLog(@"NULL sampleBuffer: %@", [error localizedDescription]);
}
};
// 拍摄静态图片
[self.imageOutput captureStillImageAsynchronouslyFromConnection:connection
completionHandler:handler];
}
- 视频
同拍照流程一样,设置捕捉会话的输出Output实例是AVCaptureMovieFileOutput类型. 具体摄像代码如下:
- (void)startRecording {
if (!self.movieOutput.isRecording) { // 是否在录制中
// 设置录制视频方向为当前方向
AVCaptureConnection *videoConnection =
[self.movieOutput connectionWithMediaType:AVMediaTypeVideo];
if ([videoConnection isVideoOrientationSupported]) {
videoConnection.videoOrientation = self.currentVideoOrientation;
}
// 设置VideoStabilization.可以提高视频质量.
if ([videoConnection isVideoStabilizationSupported]) {
if ([[[UIDevice currentDevice] systemVersion] floatValue] < 8.0) {
videoConnection.enablesVideoStabilizationWhenAvailable = YES;
} else {
videoConnection.preferredVideoStabilizationMode = AVCaptureVideoStabilizationModeAuto;
}
}
AVCaptureDevice *device = self.activeVideoInput.device;
// 设置平滑对焦模式,提升移动录制质量
if (device.isSmoothAutoFocusSupported) {
NSError *error;
if ([device lockForConfiguration:&error]) {
device.smoothAutoFocusEnabled = NO;
[device unlockForConfiguration];
} else {
[self.delegate deviceConfigurationFailedWithError:error];
}
}
NSURL *outputURL = [self uniqueURL]; // 定义视频文件唯一输出路径.
// 最后,开始录制. 通过AVCaptureFileOutputRecordingDelegate控制录制过程.
[self.movieOutput startRecordingToOutputFileURL:outputURL
recordingDelegate:self];
}
}
AVCaptureMovieFileOutput支持分段捕捉.
