AVCaptureSession获取摄像头视频及buffer（可用来自定义相机）

发现自己真的很懒，很久都不想写文章（主要是不知道写什么，太难的不会，太简单的又感觉没必要）

这篇文章的初衷是为了获取涉嫌头取到的视频buffer以和本地视频的buffer通过OpenGL混合叠加，跟上一篇是姊妹篇：AVPlayer实现播放视频和AVFoundation获取视频的buffer
还是先上效果图：

效果图.gif

1、创建session

// 1 创建session
_captureSession = [[AVCaptureSession alloc]init];
// 设置视频质量，这里根据自己需要设置；
_captureSession.sessionPreset = AVCaptureSessionPreset640x480;

2、拿到设备的摄像头

// 2 device
    _device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    _device =  [self getCameraDeviceWithPosition:AVCaptureDevicePositionBack];
/**
 取得摄像头的方向

 @param position 摄像头方向
 @return 摄像头
 */
-(AVCaptureDevice *)getCameraDeviceWithPosition:(AVCaptureDevicePosition )position{
    
    NSArray *cameras = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
    
    for (AVCaptureDevice *camera in cameras) {
        
        if ([camera position]==position) {
            
            return camera;
            
        }
    }
    return nil;
    
}

3、创建并添加input

// 3 input
    NSError *deviceError = nil;
   AVCaptureDeviceInput *input = [[AVCaptureDeviceInput alloc]initWithDevice:_device error:&deviceError];
    // 4 add input
    if ([_captureSession canAddInput:input]) {
        [_captureSession addInput:input];
    }else{
        NSLog(@"创建失败了,%@",deviceError);
        return;
    }

4、添加Video Out

    // 5 video out
    
   dispatch_queue_t queue =  dispatch_queue_create("cameraQueue", NULL);
    
    AVCaptureVideoDataOutput *videoOut = [[AVCaptureVideoDataOutput alloc]init];
    
    [videoOut setSampleBufferDelegate:self queue:queue];
    
    videoOut.alwaysDiscardsLateVideoFrames = NO;

5、设置视频格式

可以根据自己的需要设置，视频设置是一个字典形式的设置

    // 6 视频格式设置
//    [videoOut setVideoSettings:@{(id)kCVPixelBufferPixelFormatTypeKey:@(kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange)}];
    
    [videoOut connectionWithMediaType:AVMediaTypeVideo];

6、添加输出 并显示预览

这里将_prevLayer设置成属性是为了后续调节Frame，我是在viewDidLoad中加载的摄像头，所以View的frame可能还不准确，frame我在

    // 7 添加输出
    if ([_captureSession canAddOutput:videoOut]) {
        [_captureSession addOutput:videoOut];
    }
//    self.mGLView.isFullYUVRange = YES;

    AVCaptureConnection *connection = [videoOut connectionWithMediaType:AVMediaTypeVideo];
    [connection setVideoOrientation:AVCaptureVideoOrientationPortraitUpsideDown];
    [_captureSession startRunning];
    // 8 预览的layer
    _prevLayer = [AVCaptureVideoPreviewLayer layerWithSession: _captureSession];
    
//    _prevLayer.frame = self.view.bounds;
    
    _prevLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;

    [self.view.layer addSublayer: _prevLayer];
// 不要忘了在viewDidLayoutSubviews中给prevLayer的frame赋值
-(void)viewDidLayoutSubviews{
    _prevLayer.frame = self.view.bounds;
}

实现AVCaptureVideoDataOutputSampleBufferDelegate的代理方法拿到buffer做进一步处理

-(void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection{
    
     CVPixelBufferRef pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
    
//     int width1 = (int)CVPixelBufferGetWidth(pixelBuffer);
//     
//     int height1 = (int)CVPixelBufferGetHeight(pixelBuffer);
//     
//     NSLog(@"video width: %d  height: %d", width1, height1);
// 拿到某一帧可以转换为图片保存起来，跟直接照相功能相似，也可以拿到某段时间内的视频帧，保存成视频
//    或者做一些其他美颜之类的处理等待；
//    NSLog(@"在这里获得video sampleBuffer，做进一步处理（编码H.264）");
    
//     [self.mGLView displayPixelBuffer:pixelBuffer];
    //    [pool drain];
    
}