c# directshow如何实现视频的裁剪与缩放功能

要实现视频的裁剪与缩放功能，可以使用DirectShow中的视频处理滤镜。以下是一个简单示例代码，演示如何使用DirectShow实现视频的裁剪与缩放功能：

using DirectShowLib;  private void ProcessVideo(string inputFile, string outputFile, int startX, int startY, int width, int height, int newWidth, int newHeight) {     // 创建FilterGraph对象     IFilterGraph2 filterGraph = new FilterGraph() as IFilterGraph2;      // 创建SourceFilter对象     IBaseFilter sourceFilter = null;     filterGraph.AddSourceFilter(inputFile, "source", out sourceFilter);      // 创建SampleGrabber对象     ISampleGrabber sampleGrabber = new SampleGrabber() as ISampleGrabber;     sampleGrabber.SetMediaType(new AMMediaType { majorType = MediaType.Video });     filterGraph.AddFilter(sampleGrabber as IBaseFilter, "sampleGrabber");      // 创建VideoRenderer对象     IBaseFilter videoRenderer = new VideoRenderer() as IBaseFilter;     filterGraph.AddFilter(videoRenderer, "VideoRenderer");      // 设置SampleGrabber回调函数     sampleGrabber.SetCallback(new SampleGrabberCallback(startX, startY, width, height, newWidth, newHeight));      // 连接滤镜     DirectShowUtils.ConnectFilters(filterGraph, sourceFilter, sampleGrabber as IPin);     DirectShowUtils.ConnectFilters(filterGraph, sampleGrabber as IPin, videoRenderer as IPin);      // 渲染视频     IMediaControl mediaControl = filterGraph as IMediaControl;     mediaControl.Run();      // 等待视频播放完成     while (true)     {         Thread.Sleep(1000);         if (mediaControl.GetState(100, out FilterState state) == 0 && state == FilterState.Stopped)         {             break;         }     }      // 保存视频     filterGraph.RemoveFilter(videoRenderer as IBaseFilter);     filterGraph.RemoveFilter(sampleGrabber as IBaseFilter);     filterGraph.RemoveFilter(sourceFilter);     filterGraph = null; } 

在以上代码中，我们首先创建了一个FilterGraph对象，然后添加视频源Filter和SampleGrabber Filter，再添加VideoRenderer Filter。接着设置SampleGrabber的回调函数，用于处理视频帧的裁剪与缩放操作。最后，连接滤镜并运行视频，等待视频播放完成后保存视频。

需要注意的是，SampleGrabberCallback类需要根据实际需求实现视频帧的裁剪与缩放逻辑。在这个回调函数中，可以通过读取视频帧的像素数据进行处理，并将处理后的视频帧传递给下一个滤镜。