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。