iOS音视频采集笔记

2016-07-22

最近利用空余时间研究了一下音视频采集，为方便项目的参考，特意做个笔记记录。用到AVCaptureSession来进行音视频数据采集，AVCaptureSession是用来管理视频与数据的捕获,采集到音频原始数据pcm(pcm是指未经过压缩处理的)压缩为aac格式，采集到yuv420格式的视频帧压缩成h.264格式。
链接: demo链接

音视频数据采集

//初始化AVCaptureSession
 AVCaptureSession *session = [[AVCaptureSession alloc] init];
//设置录像分辨率
 [session canSetSessionPreset:AVCaptureSessionPreset640x480];
//开始配置
 [session beginConfiguration];
//获取视频设备对象
 AVCaptureDevice *videoDevice；
 NSArray *devices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
 for(AVCaptureDevice *device in devices) {
  	if (device.position == AVCaptureDevicePositionFront) {
         videoDevice = device;//前置摄像头
       }
  }
//初始化视频捕获输入对象
 NSError *error;
 AVCaptureDeviceInput *videoInput =  [[AVCaptureDeviceInput alloc]   initWithDevice:self.videoDevice error:&error];
 if (error) {
   NSLog(@"摄像头错误");
    return;
 }
//输入对象添加到Session
 if ([session canAddInput:videoInput]) {
	 [session addInput:videoInput];
 }
//输出对象
 AVCaptureVideoDataOutput *videoOutput = [[AVCaptureVideoDataOutput alloc] init];
//是否允许卡顿时丢帧
 videoOutput.alwaysDiscardsLateVideoFrames = NO;
// 设置像素格式
 [videoOutput setVideoSettings:@{
                                         (__bridge NSString *)kCVPixelBufferPixelFormatTypeKey:@(kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange)
                                         }];
//将输出对象添加到队列、并设置代理
 dispatch_queue_t captureQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
 [videoOutput setSampleBufferDelegate:self queue:captureQueue];
//session添加输出对象
 if ([session canAddOutput:self.videoOutput]) {
	[session addOutput:self.videoOutput];
 }
//创建连接  AVCaptureConnection输入对像和捕获输出对象之间建立连接。
 AVCaptureConnection *connection = [videoOutput connectionWithMediaType:AVMediaTypeVideo];
//视频的方向
 connection.videoOrientation = AVCaptureVideoOrientationPortrait;
//设置稳定性，判断connection连接对象是否支持视频稳定
 if ([connection isVideoStabilizationSupported]) {
//这个稳定模式最适合连接
	 connection.preferredVideoStabilizationMode = AVCaptureVideoStabilizationModeAuto;
	}
//缩放裁剪系数
 connection.videoScaleAndCropFactor = connection.videoMaxScaleAndCropFactor;
//***音频设置
 NSError *error;
//获取音频设备对象
 AVCaptureDevice *audioDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio];
//初始化捕获输入对象
 AVCaptureDeviceInput *audioInput = [[AVCaptureDeviceInput alloc] initWithDevice:self.audioDevice error:&error];
 if (error) {
   NSLog(@"== 录音设备出错");
  }
// 添加音频输入对象到session
 if ([session canAddInput:audioInput]) {
   [session addInput:audioInput];
  }
//初始化输出捕获对象
 AVCaptureAudioDataOutput *audioOutput = [[AVCaptureAudioDataOutput alloc] init];
// 添加音频输出对象到session
 if ([self.session canAddOutput:self.audioOutput]) {
	 [self.session addOutput:self.audioOutput];
 }
// 创建设置音频输出代理所需要的线程队列
 dispatch_queue_t audioQueue =  dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0);
 [self.audioOutput setSampleBufferDelegate:self queue:audioQueue];
//提交配置
 [session commitConfiguration];
//调用startRunning 
 [session startRunning]
   
******最后在回调中获取到pcm和yuv数据******
#pragma mark - AVCaptureVideoDataAndAudioDataOutputSampleBufferDelegate
- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:	(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection {
	if (captureOutput == audioOutput) {
		// 在此方法进行 AAC 软硬编码   		
   	 }else {
      // 在此方法中进行 H.264 硬软编码
     }
}
其中如果要切换摄像头需要先要锁定防止多处修改，最后解锁，重新提交配置

音视频采集到此结束，下一篇介绍VideoToollox和AudioToolbox对音视频进行硬编码。