AVCaptureSession配置采集行为并协调从输入设备到采集输出的数据流。要执行实时音视频采集，需要实例化采集会话并添加适当的输入和输出。

• AVCaptureSession：管理输入输出音视频流
• AVCaptureDevice：相机硬件的接口，用于控制硬件特性，诸如镜头的位置(前后摄像头)、曝光、闪光灯等。
• AVCaptureInput：配置输入设备，提供来自设备的数据
• AVCaptureOutput：管理输出的音视频数据流
• AVCaptureConnection：输入与输出的连接
• AVCaptureVideoPreviewLayer：显示当前相机正在采集的状况
• AVAssetWriter：将媒体数据写入到容器文件

初始化AVCaptureSession

- (AVCaptureSession *)captureSession {if (_captureSession == nil){_captureSession = [[AVCaptureSession alloc] init];if ([_captureSession canSetSessionPreset:AVCaptureSessionPresetHigh]) {_captureSession.sessionPreset = AVCaptureSessionPreset1280x720;}}return _captureSession;
}- (dispatch_queue_t)videoQueue {if (!_videoQueue) {_videoQueue = dispatch_queue_create("VideoCapture", DISPATCH_QUEUE_SERIAL);}return _videoQueue;
}

添加视频输入

- (AVCaptureDevice *)getCameraDeviceWithPosition:(AVCaptureDevicePosition )position {AVCaptureDeviceDiscoverySession *deviceDiscoverySession =  [AVCaptureDeviceDiscoverySession discoverySessionWithDeviceTypes:@[AVCaptureDeviceTypeBuiltInWideAngleCamera] mediaType:AVMediaTypeVideo position:position];for (AVCaptureDevice *device in deviceDiscoverySession.devices) {if ([device position] == position) {return device;}}return nil;
}- (void)setupVideoInput {AVCaptureDevice *captureDevice = [self getCameraDeviceWithPosition:AVCaptureDevicePositionBack];if (!captureDevice){NSLog(@"captureDevice failed");return;}NSError *error = nil;self.videoInput = [[AVCaptureDeviceInput alloc] initWithDevice:captureDevice error:&error];if (error) {NSLog(@"videoInput error:%@", error);return;}if ([self.captureSession canAddInput:self.videoInput]) {[self.captureSession addInput:self.videoInput];}
}

添加音频输入

- (void)setupAudioInput {AVCaptureDevice *captureDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio];NSError *error = nil;self.audioInput = [[AVCaptureDeviceInput alloc] initWithDevice:captureDevice error:&error];if (error) {NSLog(@"audioInput error:%@", error);return;}if ([self.captureSession canAddInput:self.audioInput]) {[self.captureSession addInput:self.audioInput];}
}

添加视频输出

- (void)setupVideoOutput {self.videoOutput = [[AVCaptureVideoDataOutput alloc] init];self.videoOutput.alwaysDiscardsLateVideoFrames = YES;[self.videoOutput setSampleBufferDelegate:self queue:self.videoQueue];if ([self.captureSession canAddOutput:self.videoOutput]) {[self.captureSession addOutput:self.videoOutput];}
}

添加音频输出

- (void)setupAudioOutput {self.audioOutput = [[AVCaptureAudioDataOutput alloc] init];[self.audioOutput setSampleBufferDelegate:self queue:self.videoQueue];if ([self.captureSession canAddOutput:self.audioOutput]) {[self.captureSession addOutput:self.audioOutput];}
}

设置视频预览

- (void)setupCaptureVideoPreviewLayer:(UIView *)previewView {_captureVideoPreviewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:self.captureSession];CALayer *layer = previewView.layer;_captureVideoPreviewLayer.frame = previewView.bounds;_captureVideoPreviewLayer.videoGravity = AVLayerVideoGravityResizeAspect;_captureVideoPreviewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;_captureVideoPreviewLayer.connection.videoOrientation = AVCaptureVideoOrientationLandscapeRight;[layer insertSublayer:_captureVideoPreviewLayer atIndex:0];
}

开始和结束采集会话

- (void)startSession {if (![self.captureSession isRunning]) {[self.captureSession startRunning];}
}- (void)stopSession{if ([self.captureSession isRunning]) {[self.captureSession stopRunning];}
}

初始化AVAssetWriter，将音视频保存到视频文件

- (void)setUpWriter {if (self.videoURL == nil) {return;}self.assetWriter = [AVAssetWriter assetWriterWithURL:self.videoURL fileType:AVFileTypeMPEG4 error:nil];NSInteger numPixels = kScreenWidth * kScreenHeight;CGFloat bitsPerPixel = 12.0;NSInteger bitsPerSecond = numPixels * bitsPerPixel;NSDictionary *compressionProperties = @{ AVVideoAverageBitRateKey : @(bitsPerSecond),AVVideoExpectedSourceFrameRateKey : @(15),AVVideoMaxKeyFrameIntervalKey : @(15),AVVideoProfileLevelKey : AVVideoProfileLevelH264BaselineAutoLevel };self.videoCompressionSettings = @{ AVVideoCodecKey : AVVideoCodecTypeH264,AVVideoWidthKey : @(width * 2),AVVideoHeightKey : @(height * 2),AVVideoScalingModeKey : AVVideoScalingModeResizeAspect,AVVideoCompressionPropertiesKey : compressionProperties };_assetWriterVideoInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:self.videoCompressionSettings];_assetWriterVideoInput.expectsMediaDataInRealTime = YES;self.audioCompressionSettings = @{ AVEncoderBitRatePerChannelKey : @(28000),AVFormatIDKey : @(kAudioFormatMPEG4AAC),AVNumberOfChannelsKey : @(1),AVSampleRateKey : @(22050) };_assetWriterAudioInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeAudio outputSettings:self.audioCompressionSettings];_assetWriterAudioInput.expectsMediaDataInRealTime = YES;if ([_assetWriter canAddInput:_assetWriterVideoInput]){[_assetWriter addInput:_assetWriterVideoInput];}else{NSLog(@"AssetWriter videoInput append Failed");}if ([_assetWriter canAddInput:_assetWriterAudioInput]){[_assetWriter addInput:_assetWriterAudioInput];}else{NSLog(@"AssetWriter audioInput Append Failed");}_canWrite = NO;
}

AVCaptureVideoDataOutputSampleBufferDelegate和AVCaptureAudioDataOutputSampleBufferDelegate音视频处理

#pragma mark - AVCaptureVideoDataOutputSampleBufferDelegate|AVCaptureAudioDataOutputSampleBufferDelegate
- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection {@autoreleasepool{if (connection == [self.videoOutput connectionWithMediaType:AVMediaTypeVideo]) {@synchronized(self){[self appendSampleBuffer:sampleBuffer ofMediaType:AVMediaTypeVideo];}}if (connection == [self.audioOutput connectionWithMediaType:AVMediaTypeAudio]) {@synchronized(self) {[self appendSampleBuffer:sampleBuffer ofMediaType:AVMediaTypeAudio];}}}
}- (void)appendSampleBuffer:(CMSampleBufferRef)sampleBuffer ofMediaType:(NSString *)mediaType {if (sampleBuffer == NULL){NSLog(@"empty sampleBuffer");return;}@autoreleasepool{if (!self.canWrite && mediaType == AVMediaTypeVideo){[self.assetWriter startWriting];[self.assetWriter startSessionAtSourceTime:CMSampleBufferGetPresentationTimeStamp(sampleBuffer)];self.canWrite = YES;}if (mediaType == AVMediaTypeVideo){if (self.assetWriterVideoInput.readyForMoreMediaData){BOOL success = [self.assetWriterVideoInput appendSampleBuffer:sampleBuffer];if (!success){NSLog(@"assetWriterVideoInput appendSampleBuffer fail");@synchronized (self){[self stopVideoRecorder];}}}}if (mediaType == AVMediaTypeAudio){if (self.assetWriterAudioInput.readyForMoreMediaData){BOOL success = [self.assetWriterAudioInput appendSampleBuffer:sampleBuffer];if (!success){NSLog(@"assetWriterAudioInput appendSampleBuffer fail");@synchronized (self){[self stopVideoRecorder];}}}}}
}

停止视频录制

- (void)stopVideoRecorder {__weak __typeof(self)weakSelf = self;if(_assetWriter && _assetWriter.status == AVAssetWriterStatusWriting) {[_assetWriter finishWritingWithCompletionHandler:^{weakSelf.canWrite = NO;weakSelf.assetWriter = nil;weakSelf.assetWriterAudioInput = nil;weakSelf.assetWriterVideoInput = nil;}];}
}