要實現視頻的裁剪與縮放功能，可以使用DirectShow中的視頻處理濾鏡。以下是一個簡單示例代碼，演示如何使用DirectShow實現視頻的裁剪與縮放功能：

using DirectShowLib;

private void ProcessVideo(string inputFile, string outputFile, int startX, int startY, int width, int height, int newWidth, int newHeight)
{
    // 創建FilterGraph對象
    IFilterGraph2 filterGraph = new FilterGraph() as IFilterGraph2;

    // 創建SourceFilter對象
    IBaseFilter sourceFilter = null;
    filterGraph.AddSourceFilter(inputFile, "source", out sourceFilter);

    // 創建SampleGrabber對象
    ISampleGrabber sampleGrabber = new SampleGrabber() as ISampleGrabber;
    sampleGrabber.SetMediaType(new AMMediaType { majorType = MediaType.Video });
    filterGraph.AddFilter(sampleGrabber as IBaseFilter, "sampleGrabber");

    // 創建VideoRenderer對象
    IBaseFilter videoRenderer = new VideoRenderer() as IBaseFilter;
    filterGraph.AddFilter(videoRenderer, "VideoRenderer");

    // 設置SampleGrabber回調函數
    sampleGrabber.SetCallback(new SampleGrabberCallback(startX, startY, width, height, newWidth, newHeight));

    // 連接濾鏡
    DirectShowUtils.ConnectFilters(filterGraph, sourceFilter, sampleGrabber as IPin);
    DirectShowUtils.ConnectFilters(filterGraph, sampleGrabber as IPin, videoRenderer as IPin);

    // 渲染視頻
    IMediaControl mediaControl = filterGraph as IMediaControl;
    mediaControl.Run();

    // 等待視頻播放完成
    while (true)
    {
        Thread.Sleep(1000);
        if (mediaControl.GetState(100, out FilterState state) == 0 && state == FilterState.Stopped)
        {
            break;
        }
    }

    // 保存視頻
    filterGraph.RemoveFilter(videoRenderer as IBaseFilter);
    filterGraph.RemoveFilter(sampleGrabber as IBaseFilter);
    filterGraph.RemoveFilter(sourceFilter);
    filterGraph = null;
}

在以上代碼中，我們首先創建了一個FilterGraph對象，然后添加視頻源Filter和SampleGrabber Filter，再添加VideoRenderer Filter。接著設置SampleGrabber的回調函數，用于處理視頻幀的裁剪與縮放操作。最后，連接濾鏡并運行視頻，等待視頻播放完成后保存視頻。

需要注意的是，SampleGrabberCallback類需要根據實際需求實現視頻幀的裁剪與縮放邏輯。在這個回調函數中，可以通過讀取視頻幀的像素數據進行處理，并將處理后的視頻幀傳遞給下一個濾鏡。