视频采集渲染思路

  1. 利用AVFoundation采集图像数据并进行数据缓存
  2. 通过代理返回的CMSampleBufferRef对象,捕获视频帧数据
  3. 根据像素缓存区创建Metal纹理处理缓存区,再渲染处理过的纹理数据

视频采集

  • 先创建MetalKitView,再创建纹理缓存区
- (void)createMetalKitView
{
    
    _mtkView= [[MTKView alloc] initWithFrame:self.view.frame];
    _mtkView.device = MTLCreateSystemDefaultDevice();
    [self.view addSubview:_mtkView];

    _render = [[Renderer alloc] initWithMetalKitView:_mtkView];
    _mtkView.delegate = _render;
    // 允许读写操作
    _mtkView.framebufferOnly = NO;
    /**
     创建纹理缓存区
     参数1: allocator 内存分配器.默认即可.NULL
     参数2: cacheAttributes 缓存区行为字典.默认为NULL
     参数3: metalDevice
     参数4: textureAttributes 缓存创建纹理选项的字典. 使用默认选项NULL
     参数5: cacheOut 返回时,包含新创建的纹理缓存。
     */
    CVMetalTextureCacheCreate(NULL, NULL, _mtkView.device, NULL, &_textureCache);
}

视频渲染

  • 设置摄像采集

- (void)setCaptureSession
{
    // 1.创建mCaptureSession
    self.mCaptureSession = [[AVCaptureSession alloc] init];
    
    // 2.设置视频采集分辨率
    self.mCaptureSession.sessionPreset = AVCaptureSessionPreset1920x1080;
    
    // 3.创建串行队列
    self.mProcessQueue = dispatch_queue_create("the process queue", DISPATCH_QUEUE_SERIAL);
    
    // 4.获取摄像头设备-前置or后置
    NSArray * devices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
    AVCaptureDevice * inputCamera = nil;
    for (AVCaptureDevice * device in devices) {
        if ([device position] == AVCaptureDevicePositionBack) {
            inputCamera = device;
        }
    }
    // 5.将AVCaptureDevice 转换为AVCaptureDeviceInput
    self.mCaptureDeviceInput = [[AVCaptureDeviceInput alloc] initWithDevice:inputCamera error:nil];
    
    // 6.将设备添加到MCaptureSession中
    if ([self.mCaptureSession canAddInput:self.mCaptureDeviceInput]) {
        
        [self.mCaptureSession addInput:self.mCaptureDeviceInput];
    }
    
    // 7.创建AVCaptureVideoDataOutput对象
    self.mCaptureDeviceOutput = [[AVCaptureVideoDataOutput alloc] init];
    
    // 8.设置视频延迟是否采取丢帧策略
    // yes: 处理现有帧的调度队列在captureOutput:didOutputSampleBuffer:FromConnection:Delegate方法中被阻止时,对象会立即丢弃捕获的帧。
    // NO:在丢弃新帧之前,允许委托有更多的时间处理旧帧,但这样可能会内存增加.
    [self.mCaptureDeviceOutput setAlwaysDiscardsLateVideoFrames:NO];
    // 9.设置BGRA格式,
    
    NSDictionary * videoDic = [NSDictionary dictionaryWithObject:[NSNumber numberWithInt:kCVPixelFormatType_32BGRA] forKey:(id)kCVPixelBufferPixelFormatTypeKey];
    
    [self.mCaptureDeviceOutput setVideoSettings:videoDic];
    
    // 10.设置视频捕捉输出的代理方法
    [self.mCaptureDeviceOutput setSampleBufferDelegate:self queue:self.mProcessQueue];
    
    // 11.添加输出
    if ([self.mCaptureSession canAddOutput:self.mCaptureDeviceOutput]) {
        
        [self.mCaptureSession addOutput:self.mCaptureDeviceOutput];
    }
    
    // 12.连接输入输出
    AVCaptureConnection * connection = [self.mCaptureDeviceOutput connectionWithMediaType:AVMediaTypeVideo];
    // 13.设置视频方向 - 必要的设置
    [connection setVideoOrientation:AVCaptureVideoOrientationPortrait];
    // 14.开始捕捉
    [self.mCaptureSession startRunning];
}
  • 视频采集回调

#pragma mark - AVFoundation Delegate
/// 视频采集方法,采集一次回调一次
/// @param output 
/// @param sampleBuffer 
/// @param connection 
- (void)captureOutput:(AVCaptureOutput *)output didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection
{
    // 1.从samplerBuffer 获取视频像素缓存区对象
    CVPixelBufferRef pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
    
    // 获取捕捉视频的宽高
    size_t height = CVPixelBufferGetHeight(pixelBuffer);
    size_t width = CVPixelBufferGetWidth(pixelBuffer);
 
    // 3.根据视频像素缓存区,创建metal纹理缓存区
    
    CVMetalTextureRef tmpTexture = NULL;
    /**
     从现有图像缓冲区创建核心视频Metal纹理缓冲区。
     参数1: allocator 内存分配器,默认kCFAllocatorDefault
     参数2: textureCache 纹理缓存区对象
     参数3: sourceImage 视频图像缓冲区
     参数4: textureAttributes 纹理参数字典.默认为NULL
     参数5: pixelFormat 图像缓存区数据的Metal 像素格式常量.注意如果MTLPixelFormatBGRA8Unorm和摄像头采集时设置的颜色格式不一致,则会出现图像异常的情况;
     参数6: width,纹理图像的宽度(像素)
     参数7: height,纹理图像的高度(像素)
     参数8: planeIndex.如果图像缓冲区是平面的,则为映射纹理数据的平面索引。对于非平面图像缓冲区忽略。
     参数9: textureOut,返回时,返回创建的Metal纹理缓冲区。
     */
    CVReturn status = CVMetalTextureCacheCreateTextureFromImage(kCFAllocatorDefault, self.textureCache, pixelBuffer, NULL, MTLPixelFormatBGRA8Unorm, width, height, 0, &tmpTexture);
    
    if (status == kCVReturnSuccess) {
        // 设置可绘制纹理的当前大小
        self.mtkView.drawableSize = CGSizeMake(width, height);
        
        // 返回纹理缓冲区的metal对象
        self.render.texture = CVMetalTextureGetTexture(tmpTexture);
        // 使用完毕,释放tmpTexture
        CFRelease(tmpTexture);
    } 
}
  • 纹理渲染

#pragma mark - MTKView Delegate
//视图渲染则会调用此方法
- (void)drawInMTKView:(MTKView *)view {
    
    if (self.texture) {
        
        // 创建指令缓存
        id commandBuffer = [self.commandQueue commandBuffer];
        
        // 将MTKView作为渲染目标
        id drawingTexture = view.currentDrawable.texture;
        
        // 可以再这里处理滤镜逻辑;
        //MetalPerformanceShaders是Metal的一个滤镜集成库
        //MPSImageGaussianBlur 高斯模糊处理;sigma:值越高越模糊
        MPSImageGaussianBlur * filter = [[MPSImageGaussianBlur alloc] initWithDevice:self.device sigma:1];
        // 对采集到的输入的纹理做处理,输出到渲染目标
        [filter encodeToCommandBuffer:commandBuffer sourceTexture:self.texture destinationTexture:drawingTexture];
        
        // 显示纹理
        [commandBuffer presentDrawable:view.currentDrawable];
        // 提交命令
        [commandBuffer commit];
        // 清空当前纹理准备下次的数据读取
        self.texture = NULL;
    }
}

github 工程

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