前言
承接上篇的《AV Foundation开发秘籍——实践掌握iOS & OS X应用的视听处理技术 阅读指南》 今天这篇给大家讲解下如何利用AVFoundation设计一套通用稳定的音视频框架。
核心
AVCaptureSession开启捕获任务，配置AVCaptureDeviceInput定制捕获任务的输入源（多种摄像头），通过AVFoundation内各种Data output输出数据（元数据、视频帧、音频帧），AVAssetWriter开启写任务，将音视频数据归档为媒体文件。
实现功能
视频流预览、录像归档、捕获相片、切换摄像头、人脸检测、帧率配置、相机详细配置
框架源码
具体设计
核心模块 XDCaptureService & XDVideoWritter
XDCaptureService是对外API的总入口，也是框架的核心类，主要做音视频输入输出配置工作和调度工作。 XDVideoWritter是音视频写模块，主要提供写数据和归档数据的基础操作，不对外暴露。 对外API设计：
@class XDCaptureService;
@protocol XDCaptureServiceDelegate <NSObject>
@optional
//service生命周期
- (void)captureServiceDidStartService:(XDCaptureService *)service;
- (void)captureService:(XDCaptureService *)service serviceDidFailWithError:(NSError *)error;
- (void)captureServiceDidStopService:(XDCaptureService *)service;
- (void)captureService:(XDCaptureService *)service getPreviewLayer:(AVCaptureVideoPreviewLayer *)previewLayer;
- (void)captureService:(XDCaptureService *)service outputSampleBuffer:(CMSampleBufferRef)sampleBuffer;
//录像相关
- (void)captureServiceRecorderDidStart:(XDCaptureService *)service ;
- (void)captureService:(XDCaptureService *)service recorderDidFailWithError:(NSError *)error;
- (void)captureServiceRecorderDidStop:(XDCaptureService *)service;
//照片捕获
- (void)captureService:(XDCaptureService *)service capturePhoto:(UIImage *)photo;
//人脸检测
- (void)captureService:(XDCaptureService *)service outputFaceDetectData:(NSArray <AVMetadataFaceObject*>*) faces;
//景深数据
- (void)captureService:(XDCaptureService *)service captureTrueDepth:(AVDepthData *)depthData API_AVAILABLE(ios(11.0));
@end
@protocol XDCaptureServicePreViewSource <NSObject>
- (AVCaptureVideoPreviewLayer *)preViewLayerSource;
@end
@interface XDCaptureService : NSObject
//是否录制音频，默认是NO
@property (nonatomic, assign) BOOL shouldRecordAudio;
//iOS原生人脸检测，默认是NO
@property (nonatomic, assign) BOOL openNativeFaceDetect;
//摄像头的方向，默认是AVCaptureDevicePositionFront（前置）
@property (nonatomic, assign) AVCaptureDevicePosition devicePosition;
//判断是否支持景深模式，当前只支持7p、8p、X的后置摄像头及X的前后摄像头,系统要求是iOS 11以上
@property (nonatomic, assign, readonly) BOOL depthSupported;
//是否开启景深模式，默认是NO
@property (nonatomic, assign) BOOL openDepth;
//只有以下指定的sessionPreset才有depth数据：AVCaptureSessionPresetPhoto、AVCaptureSessionPreset1280x720、AVCaptureSessionPreset640x480
@property (nonatomic, assign) AVCaptureSessionPreset sessionPreset;
//帧率，默认是30
@property (nonatomic, assign) int frameRate;
//录像的临时存储地址，建议每次录完视频做下重定向
@property (nonatomic, strong, readonly) NSURL *recordURL;
//如果设置preViewSource则内部不生成AVCaptureVideoPreviewLayer
@property (nonatomic, assign) id<XDCaptureServicePreViewSource> preViewSource;
@property (nonatomic, assign) id<XDCaptureServiceDelegate> delegate;
@property (nonatomic, assign, readonly) BOOL isRunning;
//视频编码设置（影响录制的视频的编码和大小）
@property (nonatomic, strong) NSDictionary *videoSetting;
///相机专业设置，除非特定需求，一般不设置
//感光度（iOS8以上）
@property (nonatomic, assign, readonly) CGFloat deviceISO;
@property (nonatomic, assign, readonly) CGFloat deviceMinISO;
@property (nonatomic, assign, readonly) CGFloat deviceMaxISO;
//镜头光圈大小
@property (nonatomic, assign, readonly) CGFloat deviceAperture;
//曝光
@property (nonatomic, assign, readonly) BOOL supportsTapToExpose;
@property (nonatomic, assign) AVCaptureExposureMode exposureMode;
@property (nonatomic, assign) CGPoint exposurePoint;
@property (nonatomic, assign, readonly) CMTime deviceExposureDuration;
//聚焦
@property (nonatomic, assign, readonly) BOOL supportsTapToFocus;
@property (nonatomic, assign) AVCaptureFocusMode focusMode;
@property (nonatomic, assign) CGPoint focusPoint;
//白平衡
@property (nonatomic, assign) AVCaptureWhiteBalanceMode whiteBalanceMode;
//手电筒
@property (nonatomic, assign, readonly) BOOL hasTorch;
@property (nonatomic, assign) AVCaptureTorchMode torchMode;
//闪光灯
@property (nonatomic, assign, readonly) BOOL hasFlash;
@property (nonatomic, assign) AVCaptureFlashMode flashMode;
//相机权限判断
+ (BOOL)videoGranted;
//麦克风权限判断
+ (BOOL)audioGranted;
//切换摄像机
- (void)switchCamera;
//启动
- (void)startRunning;
//关闭
- (void)stopRunning;
//开始录像
- (void)startRecording;
//取消录像
- (void)cancleRecording;
//停止录像
- (void)stopRecording;
//拍照
- (void)capturePhoto;
@end
复制代码CDG队列分流
因为在主线程启动音视频捕获及音视频读写会阻塞主线程，所以我们需要将这些任务派发到子线程中执行。我们选择GCD队列帮我们做这个视频。我们框架总共配置3个队列，分别是sessionQueue、writtingQueue、outputQueue，这些队列都是串行队列，因为音视频相关操作都是有顺序（时序）要求，保证当前队列只有一个操作的执行（配置、写数据、读数据）。sessionQueue主要负责音视频任务启动的调度，writtingQueue主要负责写数据的调度，保证数据帧能够准确归档到文件，outputQueue主要负责数据帧的输出。
@property (nonatomic, strong) dispatch_queue_t sessionQueue;
@property (nonatomic, strong) dispatch_queue_t writtingQueue;
@property (nonatomic, strong) dispatch_queue_t outputQueue;
_sessionQueue = dispatch_queue_create("com.caixindong.captureservice.session", DISPATCH_QUEUE_SERIAL);
_writtingQueue = dispatch_queue_create("com.caixindong.captureservice.writting", DISPATCH_QUEUE_SERIAL);
_outputQueue = dispatch_queue_create("com.caixindong.captureservice.output", DISPATCH_QUEUE_SERIAL);
复制代码音视频捕获
初始化捕获任务
sessionPreset指定了输出的视频帧的像素，例如640*480
@property (nonatomic, strong) AVCaptureSession *captureSession;
_captureSession = [[AVCaptureSession alloc] init];
_captureSession.sessionPreset = _sessionPreset;
复制代码配置捕获的输入
获取输入源设备，通过_cameraWithPosition可以获取摄像头的抽象表示，因为红外摄像头、双摄像头只能从较新API中获取，所以方法里已经做了兼容处理。并用输入源设备配置捕获输入AVCaptureDeviceInput
@property (nonatomic, strong) AVCaptureDeviceInput *videoInput;
- (BOOL)_setupVideoInputOutput:(NSError **) error {
self.currentDevice = [self _cameraWithPosition:_devicePosition];
self.videoInput = [[AVCaptureDeviceInput alloc] initWithDevice:_currentDevice error:error];
if (_videoInput) {
if ([_captureSession canAddInput:_videoInput]) {
[_captureSession addInput:_videoInput];
} else {
*error = [NSError errorWithDomain:@"com.caixindong.captureservice.video" code:-2200 userInfo:@{NSLocalizedDescriptionKey:@"add video input fail"}];
return NO;
}
} else {
*error = [NSError errorWithDomain:@"com.caixindong.captureservice.video" code:-2201 userInfo:@{NSLocalizedDescriptionKey:@"video input is nil"}];
return NO;
}
//稳定帧率
CMTime frameDuration = CMTimeMake(1, _frameRate);
if ([_currentDevice lockForConfiguration:error]) {
_currentDevice.activeVideoMaxFrameDuration = frameDuration;
_currentDevice.activeVideoMinFrameDuration = frameDuration;
[_currentDevice unlockForConfiguration];
} else {
*error = [NSError errorWithDomain:@"com.caixindong.captureservice.video" code:-2203 userInfo:@{NSLocalizedDescriptionKey:@"device lock fail(input)"}];
return NO;
}
……Other code
}
- (AVCaptureDevice *)_cameraWithPosition:(AVCaptureDevicePosition)position {
if (@available(iOS 10.0, *)) {
//AVCaptureDeviceTypeBuiltInWideAngleCamera默认广角摄像头，AVCaptureDeviceTypeBuiltInTelephotoCamera长焦摄像头，AVCaptureDeviceTypeBuiltInDualCamera后置双摄像头，AVCaptureDeviceTypeBuiltInTrueDepthCamera红外前置摄像头
NSMutableArray *mulArr = [NSMutableArray arrayWithObjects:AVCaptureDeviceTypeBuiltInWideAngleCamera,AVCaptureDeviceTypeBuiltInTelephotoCamera,nil];
if (@available(iOS 10.2, *)) {
[mulArr addObject:AVCaptureDeviceTypeBuiltInDualCamera];
}
if (@available(iOS 11.1, *)) {
[mulArr addObject:AVCaptureDeviceTypeBuiltInTrueDepthCamera];
}
AVCaptureDeviceDiscoverySession *discoverySession = [AVCaptureDeviceDiscoverySession discoverySessionWithDeviceTypes:[mulArr copy] mediaType:AVMediaTypeVideo position:position];
return discoverySession.devices.firstObject;
} else {
NSArray *videoDevices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
for (AVCaptureDevice *device in videoDevices) {
if (device.position == position) {
return device;
}
}
}
return nil;
}
复制代码配置捕获输出
根据不同的功能需求，我们可以往捕获任务里添加不同的输出，例如捕获基础的视频帧数据，我们添加AVCaptureVideoDataOutput，捕获音频数据，我们添加AVCaptureAudioDataOutput，捕获人脸数据，我们添加AVCaptureMetadataOutput。因为音频的输出和视频输出的设置方式大同小异，所以这里只列出视频输出的关键代码，这里有几个关键的设计：
1、因为相机传感器问题，输出的视频流的方向会有90度偏转，所以我们需要通过获取与输出连接的videoConnection进行偏转配置； 2、视频帧（或者音频帧）都是以CMSampleBufferRef格式输出，视频帧可能经过多个业务处理，例如写文件或者抛到上层业务处理，所以处理数据前都对视频帧数据进行retatin操作，保证各个业务线处理的视频帧是独立的，具体可以看_processVideoData；
3、为了及时清理临时变量（对视频帧处理的各种操作可能需要较多内存空间），所以将外抛的帧处理用autorelease pool包裹起来，防止出现内存高峰；
@property (nonatomic, strong) AVCaptureVideoDataOutput *videoOutput;
- (BOOL)_setupVideoInputOutput:(NSError **) error {
……Other code
self.videoOutput = [[AVCaptureVideoDataOutput alloc] init];
_videoOutput.videoSettings = @{(id)kCVPixelBufferPixelFormatTypeKey: @(kCVPixelFormatType_32BGRA)};
//对迟到的帧做丢帧处理
_videoOutput.alwaysDiscardsLateVideoFrames = YES;
dispatch_queue_t videoQueue = dispatch_queue_create("com.caixindong.captureservice.video", DISPATCH_QUEUE_SERIAL);
//设置数据输出的delegate
[_videoOutput setSampleBufferDelegate:self queue:videoQueue];
if ([_captureSession canAddOutput:_videoOutput]) {
[_captureSession addOutput:_videoOutput];
} else {
*error = [NSError errorWithDomain:@"com.caixindong.captureservice.video" code:-2204 userInfo:@{NSLocalizedDescriptionKey:@"device lock fail(output)"}];
return NO;
}
self.videoConnection = [self.videoOutput connectionWithMediaType:AVMediaTypeVideo];
//录制视频会有90度偏转，是因为相机传感器问题，所以在这里设置输出的视频流的方向
if (_videoConnection.isVideoOrientationSupported) {
_videoConnection.videoOrientation = AVCaptureVideoOrientationPortrait;
}
return YES;
}
#pragma mark - AVCaptureVideoDataOutputSampleBufferDelegate && AVCaptureAudioDataOutputSampleBufferDelegate
- (void)captureOutput:(AVCaptureOutput *)output didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection {
//可以捕获到不同的线程
if (connection == _videoConnection) {
@synchronized(self) {
[self _processVideoData:sampleBuffer];
};
} else if (connection == _audioConnection) {
@synchronized(self) {
[self _processAudioData:sampleBuffer];
};
}
}
#pragma mark - process Data
- (void)_processVideoData:(CMSampleBufferRef)sampleBuffer {
//CFRetain的目的是为了每条业务线（写视频、抛帧）的sampleBuffer都是独立的
if (_videoWriter && _videoWriter.isWriting) {
CFRetain(sampleBuffer);
dispatch_async(_writtingQueue, ^{
[_videoWriter appendSampleBuffer:sampleBuffer];
CFRelease(sampleBuffer);
});
}
CFRetain(sampleBuffer);
//及时清理临时变量，防止出现内存高峰
dispatch_async(_outputQueue, ^{
@autoreleasepool{
if (self.delegate && [self.delegate respondsToSelector:@selector(captureService:outputSampleBuffer:)]) {
[self.delegate captureService:self outputSampleBuffer:sampleBuffer];
}
}
CFRelease(sampleBuffer);
});
}
复制代码配置图片数据输出
配置图片数据输出的目的是为了实现相片捕获功能，通过setOutputSettings，我们可以配置我们输出的图片格式。
@property (nonatomic, strong) AVCaptureStillImageOutput *imageOutput;
- (BOOL)_setupImageOutput:(NSError **)error {
self.imageOutput = [[AVCaptureStillImageOutput alloc] init];
NSDictionary *outputSetting = @{AVVideoCodecKey: AVVideoCodecJPEG};
[_imageOutput setOutputSettings:outputSetting];
if ([_captureSession canAddOutput:_imageOutput]) {
[_captureSession addOutput:_imageOutput];
return YES;
} else {
*error = [NSError errorWithDomain:@"com.caixindong.captureservice.image" code:-2205 userInfo:@{NSLocalizedDescriptionKey:@"device lock fail(output)"}];
return NO;
}
}
//拍照功能实现
- (void)capturePhoto {
AVCaptureConnection *connection = [_imageOutput connectionWithMediaType:AVMediaTypeVideo];
if (connection.isVideoOrientationSupported) {
connection.videoOrientation = AVCaptureVideoOrientationPortrait;
}
__weak typeof(self) weakSelf = self;
[_imageOutput captureStillImageAsynchronouslyFromConnection:connection completionHandler:^(CMSampleBufferRef _Nullable imageDataSampleBuffer, NSError * _Nullable error) {
__strong typeof(weakSelf) strongSelf = weakSelf;
if (imageDataSampleBuffer != NULL) {
NSData *imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageDataSampleBuffer];
UIImage *image = [UIImage imageWithData:imageData];
if (strongSelf.delegate && [strongSelf.delegate respondsToSelector:@selector(captureService:capturePhoto:)]) {
[strongSelf.delegate captureService:strongSelf capturePhoto:image];
}
}
}];
}
复制代码配置人脸数据输出
关键是配置人脸元数据输出AVCaptureMetadataOutput，并指定metadataObjectTypes为AVMetadataObjectTypeFace，捕获的人脸数据包含当前视频帧中所有的人脸，可以从数据中提取人脸的范围、位置、偏转角，但这个有个注意点，就是原始的人脸数据的坐标是相机坐标系，我们需要转化为屏幕坐标，这样才方便我们的业务处理，具体可以看人脸数据输出那一块。
@property (nonatomic, strong) AVCaptureMetadataOutput *metadataOutput;
-(void)captureOutput:(AVCaptureOutput *)output didOutputMetadataObjects:(NSArray<__kindof AVMetadataObject *> *)metadataObjects fromConnection:(AVCaptureConnection *)connection {
NSMutableArray *transformedFaces = [NSMutableArray array];
for (AVMetadataObject *face in metadataObjects) {
@autoreleasepool{
AVMetadataFaceObject *transformedFace = (AVMetadataFaceObject*)[self.previewLayer transformedMetadataObjectForMetadataObject:face];
if (transformedFace) {
[transformedFaces addObject:transformedFace];
}
};
}
@autoreleasepool{
if (self.delegate && [self.delegate respondsToSelector:@selector(captureService:outputFaceDetectData:)]) {
[self.delegate captureService:self outputFaceDetectData:[transformedFaces copy]];
}
};
}
复制代码配置预览源
这里有两种方式，一种是外部已经通过实现预览数据源方法配置了数据源，另外一种是内部自己生成AVCaptureVideoPreviewLayer配置为预览源。
if (self.preViewSource && [self.preViewSource respondsToSelector:@selector(preViewLayerSource)]) {
self.previewLayer = [self.preViewSource preViewLayerSource];
[_previewLayer setSession:_captureSession];
[_previewLayer setVideoGravity:AVLayerVideoGravityResizeAspectFill];
} else {
self.previewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:_captureSession];
//充满整个屏幕
[_previewLayer setVideoGravity:AVLayerVideoGravityResizeAspectFill];
if (self.delegate && [self.delegate respondsToSelector:@selector(captureService:getPreviewLayer:)]) {
[self.delegate captureService:self getPreviewLayer:_previewLayer];
}
}
复制代码处理音视频前后台状态变化
iOS的音视频前后台机制较复杂，有各种生命周期变化，为了保证我们框架在正确状态下做正确的事，我们将数据帧的读和写的状态处理进行解耦，各位维护自己的通知状态变化处理。外层业务无需监听AVFoundation的通知手动处理视频流的状态变化。 读模块音视频通知配置：
//CaptureService和VideoWritter各自维护自己的生命周期，捕获视频流的状态与写入视频流的状态解耦分离，音视频状态变迁由captureservice内部管理，外层业务无需手动处理视频流变化
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(_captureSessionNotification:) name:nil object:self.captureSession];
//为了适配低于iOS 9的版本，在iOS 9以前，当session start 还没完成就退到后台，回到前台会捕获AVCaptureSessionRuntimeErrorNotification，这时需要手动重新启动session，iOS 9以后系统对此做了优化，系统退到后台后会将session start缓存起来，回到前台会自动调用缓存的session start，无需手动调用
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(_enterForegroundNotification:) name:UIApplicationWillEnterForegroundNotification object:nil];
#pragma mark - CaptureSession Notification
- (void)_captureSessionNotification:(NSNotification *)notification {
NSLog(@"_captureSessionNotification:%@",notification.name);
if ([notification.name isEqualToString:AVCaptureSessionDidStartRunningNotification]) {
if (!_firstStartRunning) {
NSLog(@"session start running");
_firstStartRunning = YES;
if (self.delegate && [self.delegate respondsToSelector:@selector(captureServiceDidStartService:)]) {
[self.delegate captureServiceDidStartService:self];
}
} else {
NSLog(@"session resunme running");
}
} else if ([notification.name isEqualToString:AVCaptureSessionDidStopRunningNotification]) {
if (!_isRunning) {
NSLog(@"session stop running");
if (self.delegate && [self.delegate respondsToSelector:@selector(captureServiceDidStopService:)]) {
[self.delegate captureServiceDidStopService:self];
}
} else {
NSLog(@"interupte session stop running");
}
} else if ([notification.name isEqualToString:AVCaptureSessionWasInterruptedNotification]) {
NSLog(@"session was interupted, userInfo: %@",notification.userInfo);
} else if ([notification.name isEqualToString:AVCaptureSessionInterruptionEndedNotification]) {
NSLog(@"session interupted end");
} else if ([notification.name isEqualToString:AVCaptureSessionRuntimeErrorNotification]) {
NSError *error = notification.userInfo[AVCaptureSessionErrorKey];
if (error.code == AVErrorDeviceIsNotAvailableInBackground) {
NSLog(@"session runtime error : AVErrorDeviceIsNotAvailableInBackground");
_startSessionOnEnteringForeground = YES;
} else {
if (self.delegate && [self.delegate respondsToSelector:@selector(captureService:serviceDidFailWithError:)]) {
[self.delegate captureService:self serviceDidFailWithError:error];
}
}
} else {
NSLog(@"handel other notification : %@",notification.name);
}
}
#pragma mark - UIApplicationWillEnterForegroundNotification
- (void)_enterForegroundNotification:(NSNotification *)notification {
if (_startSessionOnEnteringForeground == YES) {
NSLog(@"为了适配低于iOS 9的版本，在iOS 9以前，当session start 还没完成就退到后台，回到前台会捕获AVCaptureSessionRuntimeErrorNotification，这时需要手动重新启动session，iOS 9以后系统对此做了优化，系统退到后台后会将session start缓存起来，回到前台会自动调用缓存的session start，无需手动调用");
_startSessionOnEnteringForeground = NO;
[self startRunning];
}
}
复制代码写模块音视频通知配置：
//写模块注册通知，只负责写相关的状态处理
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(_assetWritterInterruptedNotification:) name:AVCaptureSessionWasInterruptedNotification object:nil];
- (void)_assetWritterInterruptedNotification:(NSNotification *)notification {
NSLog(@"assetWritterInterruptedNotification");
[self cancleWriting];
}
复制代码启动捕获 & 关闭捕获
异步启动，防止阻塞主线程。串行队列中执行启动和关闭，保证不会出现启动到一半就关闭这种异常case。
- (void)startRunning {
dispatch_async(_sessionQueue, ^{
NSError *error = nil;
BOOL result = [self _setupSession:&error];
if (result) {
_isRunning = YES;
[_captureSession startRunning];
}else{
if (self.delegate && [self.delegate respondsToSelector:@selector(captureService:serviceDidFailWithError:)]) {
[self.delegate captureService:self serviceDidFailWithError:error];
}
}
});
}
- (void)stopRunning {
dispatch_async(_sessionQueue, ^{
_isRunning = NO;
NSError *error = nil;
[self _clearVideoFile:&error];
if (error) {
if (self.delegate && [self.delegate respondsToSelector:@selector(captureService:serviceDidFailWithError:)]) {
[self.delegate captureService:self serviceDidFailWithError:error];
}
}
[_captureSession stopRunning];
});
}
复制代码切换摄像头
切换不仅仅是切换device，同时还要将旧的捕获input移除，添加新的device input。切换摄像头时，videoConnection会变化，所以需要重新获取。
- (void)switchCamera {
if (_openDepth) {
return;
}
NSError *error;
AVCaptureDevice *videoDevice = [self _inactiveCamera];
AVCaptureDeviceInput *videoInput = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:&error];
if (videoInput) {
[_captureSession beginConfiguration];
[_captureSession removeInput:self.videoInput];
if ([self.captureSession canAddInput:videoInput]) {
[self.captureSession addInput:videoInput];
self.videoInput = videoInput;
//切换摄像头videoConnection会变化，所以需要重新获取
self.videoConnection = [self.videoOutput connectionWithMediaType:AVMediaTypeVideo];
if (_videoConnection.isVideoOrientationSupported) {
_videoConnection.videoOrientation = AVCaptureVideoOrientationPortrait;
}
} else {
[self.captureSession addInput:self.videoInput];
}
[self.captureSession commitConfiguration];
}
_devicePosition = _devicePosition == AVCaptureDevicePositionFront?AVCaptureDevicePositionBack:AVCaptureDevicePositionFront;
}
- (AVCaptureDevice *)_inactiveCamera {
AVCaptureDevice *device = nil;
if (_devicePosition == AVCaptureDevicePositionBack) {
device = [self _cameraWithPosition:AVCaptureDevicePositionFront];
} else {
device = [self _cameraWithPosition:AVCaptureDevicePositionBack];
}
return device;
}
复制代码录像功能
通过videoSetting配置录制完的视频的编码格式，框架默认的编码格式是H.264，H.264是一种高效的视频编码格式，之后再出篇文章讲下这种编码格式，现阶段你只需要知道这是一种常用的编码格式，想了解更多编码格式，可以看下AVVideoCodecType里面的内容。在XDCaptureService的startRecording方法中，我们初始化我们的写模块XDVideoWritter，XDVideoWritter根据videoSetting配置对应的编码格式。
- (void)startRecording {
dispatch_async(_writtingQueue, ^{
@synchronized(self) {
NSString *videoFilePath = [_videoDir stringByAppendingPathComponent:[NSString stringWithFormat:@"Record-%llu.mp4",mach_absolute_time()]];
_recordURL = [[NSURL alloc] initFileURLWithPath:videoFilePath];
if (_recordURL) {
_videoWriter = [[XDVideoWritter alloc] initWithURL:_recordURL VideoSettings:_videoSetting audioSetting:_audioSetting];
_videoWriter.delegate = self;
[_videoWriter startWriting];
if (self.delegate && [self.delegate respondsToSelector:@selector(captureServiceRecorderDidStart:)]) {
[self.delegate captureServiceRecorderDidStart:self];
}
} else {
NSLog(@"No record URL");
}
}
});
}
//XDVideoWritter.m
- (void)startWriting {
if (_assetWriter) {
_assetWriter = nil;
}
NSError *error = nil;
NSString *fileType = AVFileTypeMPEG4;
_assetWriter = [[AVAssetWriter alloc] initWithURL:_outputURL fileType:fileType error:&error];
if (!_assetWriter || error) {
if (self.delegate && [self.delegate respondsToSelector:@selector(videoWritter:didFailWithError:)]){
[self.delegate videoWritter:self didFailWithError:error];
}
}
if (_videoSetting) {
_videoInput = [[AVAssetWriterInput alloc] initWithMediaType:AVMediaTypeVideo outputSettings:_videoSetting];
_videoInput.expectsMediaDataInRealTime = YES;
if ([_assetWriter canAddInput:_videoInput]) {
[_assetWriter addInput:_videoInput];
} else {
NSError *error = [NSError errorWithDomain:@"com.caixindong.captureservice.writter" code:-2210 userInfo:@{NSLocalizedDescriptionKey:@"VideoWritter unable to add video input"}];
if (self.delegate && [self.delegate respondsToSelector:@selector(videoWritter:didFailWithError:)]) {
[self.delegate videoWritter:self didFailWithError:error];
}
return;
}
} else {
NSLog(@"warning: no video setting");
}
if (_audioSetting) {
_audioInput = [[AVAssetWriterInput alloc] initWithMediaType:AVMediaTypeAudio outputSettings:_audioSetting];
_audioInput.expectsMediaDataInRealTime = YES;
if ([_assetWriter canAddInput:_audioInput]) {
[_assetWriter addInput:_audioInput];
} else {
NSError *error = [NSError errorWithDomain:@"com.caixindong.captureservice.writter" code:-2211 userInfo:@{NSLocalizedDescriptionKey:@"VideoWritter unable to add audio input"}];
if (self.delegate && [self.delegate respondsToSelector:@selector(videoWritter:didFailWithError:)]) {
[self.delegate videoWritter:self didFailWithError:error];
}
return;
}
} else {
NSLog(@"warning: no audio setting");
}
if ([_assetWriter startWriting]) {
self.isWriting = YES;
} else {
NSError *error = [NSError errorWithDomain:@"com.xindong.captureservice.writter" code:-2212 userInfo:@{NSLocalizedDescriptionKey: [NSString stringWithFormat: @"VideoWritter startWriting fail error: %@",_assetWriter.error.localizedDescription]}];
if (self.delegate && [self.delegate respondsToSelector:@selector(videoWritter:didFailWithError:)]) {
[self.delegate videoWritter:self didFailWithError:error];
}
}
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(_assetWritterInterruptedNotification:) name:AVCaptureSessionWasInterruptedNotification object:nil];
}
复制代码录像的原理就是在抛数据的同时调用XDVideoWritter的appendSampleBuffer方法将数据写入一个临时文件中，当调用stopRecording，也就是调用到XDVideoWritter的stopWriting方法停止写数据，将临时文件归档为MP4文件。
- (void)stopRecording {
dispatch_async(_writtingQueue, ^{
@synchronized(self) {
if (_videoWriter) {
[_videoWriter stopWriting];
}
}
});
}
//XDVideoWritter.m
- (void)appendSampleBuffer:(CMSampleBufferRef)sampleBuffer {
CMFormatDescriptionRef formatDesc = CMSampleBufferGetFormatDescription(sampleBuffer);
CMMediaType mediaType = CMFormatDescriptionGetMediaType(formatDesc);
if (mediaType == kCMMediaType_Video) {
CMTime timestamp = CMSampleBufferGetPresentationTimeStamp(sampleBuffer);
if (self.firstSample) {
[_assetWriter startSessionAtSourceTime:timestamp];
self.firstSample = NO;
}
if (_videoInput.readyForMoreMediaData) {
if (![_videoInput appendSampleBuffer:sampleBuffer]) {
NSError *error = [NSError errorWithDomain:@"com.caixindong.captureservice.writter" code:-2213 userInfo:@{NSLocalizedDescriptionKey:[NSString stringWithFormat: @"VideoWritter appending video sample buffer fail error:%@",_assetWriter.error.localizedDescription]}];
if (self.delegate && [self.delegate respondsToSelector:@selector(videoWritter:didFailWithError:)]) {
[self.delegate videoWritter:self didFailWithError:error];
}
}
}
} else if (!self.firstSample && mediaType == kCMMediaType_Audio) {
if (_audioInput.readyForMoreMediaData) {
if (![_audioInput appendSampleBuffer:sampleBuffer]) {
NSError *error = [NSError errorWithDomain:@"com.caixindong.captureservice.writter" code:-2214 userInfo:@{NSLocalizedDescriptionKey:[NSString stringWithFormat:@"VideoWritter appending audio sample buffer fail error: %@",_assetWriter.error]}];
if (self.delegate && [self.delegate respondsToSelector:@selector(videoWritter:didFailWithError:)]) {
[self.delegate videoWritter:self didFailWithError:error];
}
}
}
}
}
- (void)stopWriting {
if (_assetWriter.status == AVAssetWriterStatusWriting) {
self.isWriting = NO;
[_assetWriter finishWritingWithCompletionHandler:^{
if (_assetWriter.status == AVAssetWriterStatusCompleted) {
if (self.delegate && [self.delegate respondsToSelector:@selector(videoWritter:completeWriting:)]) {
[self.delegate videoWritter:self completeWriting:nil];
}
} else {
if (self.delegate && [self.delegate respondsToSelector:@selector(videoWritter:completeWriting:)]) {
[self.delegate videoWritter:self completeWriting:_assetWriter.error];
}
}
}];
} else {
NSLog(@"warning : stop writing with unsuitable state : %ld",_assetWriter.status);
}
[[NSNotificationCenter defaultCenter] removeObserver:self name:AVCaptureSessionWasInterruptedNotification object:nil];
}
复制代码感谢
感觉每一位给XDCaptureService issue 和使用反馈的同学，开源完善靠大家！