为什么当我尝试使用directshow捕获视频到mp4文件时，文件是空的

当我退出程序时，mp4文件自动删除。

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using DirectShowLib;
using DirectShowLib.BDA;
using DirectShowLib.DES;
using DirectShowLib.DMO;
using DirectShowLib.Dvd;
using DirectShowLib.MultimediaStreaming;
using DirectShowLib.SBE;
using System.Runtime.InteropServices;
using System.Management;
using System.IO;
using AForge.Video;
using AForge.Video.DirectShow;
using AForge.Video.FFMPEG;
using AForge.Video.VFW;
using System.Drawing.Imaging;

namespace Youtube_Manager
{
    public partial class Elgato_Video_Capture : Form
    {
        IFileSinkFilter sink;
        IFilterGraph2 graph;
        ICaptureGraphBuilder2 captureGraph;
        Size videoSize;
        string error = "";
        List<Object> devices = new List<Object>();
        IMediaControl mediaControl;
        public Elgato_Video_Capture()
        {
            InitializeComponent();
            if (comboBox1.Items.Count == 0)
            {
                for (int xx = 1; xx <= 8; xx++)
                {
                    comboBox1.Items.Add(xx);
                }
            }
            InitDevice();
        }
        IPin outPin;
        IPin inPin;
        private void InitDevice()
        {
            try
            {
                //Set the video size to use for capture and recording
                videoSize = new Size(827, 505);//1280, 720);
                //Initialize filter graph and capture graph
                graph = (IFilterGraph2)new FilterGraph();
                captureGraph = (ICaptureGraphBuilder2)new CaptureGraphBuilder2();
                captureGraph.SetFiltergraph(graph);
                //Create filter for Elgato
                Guid elgatoGuid = new Guid("39F50F4C-99E1-464A-B6F9-D605B4FB5918");
                Type comType = Type.GetTypeFromCLSID(elgatoGuid);
                IBaseFilter  elgatoFilter = (IBaseFilter)Activator.CreateInstance(comType);
                graph.AddFilter(elgatoFilter, "Elgato Video Capture Filter");
                //Create smart tee filter, add to graph, connect Elgato's video out to smart tee in
                IBaseFilter smartTeeFilter = (IBaseFilter)new SmartTee();
                graph.AddFilter(smartTeeFilter, "Smart Tee");
                outPin = GetPin(elgatoFilter, "Video");
                inPin = GetPin(smartTeeFilter, "Input");               
                graph.Connect(outPin, inPin);
                //Create video renderer filter, add it to graph, connect smartTee Preview pin to video renderer's input pin
                IBaseFilter videoRendererFilter = (IBaseFilter)new VideoRenderer();
                graph.AddFilter(videoRendererFilter, "Video Renderer");
                outPin = GetPin(smartTeeFilter, "Capture");
                inPin = GetPin(videoRendererFilter, "Input");
                graph.Connect(outPin, inPin);
                captureGraph.SetOutputFileName(MediaSubType.Avi, @"e:'screenshots'test1.mp4", out smartTeeFilter, out sink);
                sink.SetFileName(@"e:'screenshots'test1.mp4", null);
                //Render stream from video renderer
                captureGraph.RenderStream(PinCategory.Capture, MediaType.Video, videoRendererFilter, null, null);
                //Set the video preview to be the videoFeed panel
                IVideoWindow vw = (IVideoWindow)graph;
                vw.put_Owner(pictureBox1.Handle);
                vw.put_MessageDrain(this.Handle);
                vw.put_WindowStyle(WindowStyle.Child | WindowStyle.ClipSiblings | WindowStyle.ClipChildren);
                vw.SetWindowPosition(0, 0, 827, 505);
                //Start the preview
                mediaControl = graph as IMediaControl;
                mediaControl.Run();
            }
            catch (Exception err)
            {
                error = err.ToString();
            }
        }
         IPin GetPin(IBaseFilter filter, string pinname)
        {
            IEnumPins epins;
            int hr = filter.EnumPins(out epins);
            checkHR(hr, "Can't enumerate pins");
            IntPtr fetched = Marshal.AllocCoTaskMem(4);
            IPin[] pins = new IPin[1];
            while (epins.Next(1, pins, fetched) == 0)
            {
                PinInfo pinfo;
                pins[0].QueryPinInfo(out pinfo);
                bool found = (pinfo.name == pinname);
                DsUtils.FreePinInfo(pinfo);
                if (found)
                    return pins[0];
            }
            checkHR(-1, "Pin not found");
            return null;
        }
        public  void checkHR(int hr, string msg)
        {
            if (hr < 0)
            {
                MessageBox.Show(msg);
                DsError.ThrowExceptionForHR(hr);
            }            
        }
}

我现在将这部分添加到我的代码中:

captureGraph.SetOutputFileName(MediaSubType.Avi, @"e:'screenshots'test1.mp4", out smartTeeFilter, out sink);
sink.SetFileName(@"e:'screenshots'test1.mp4", null);

我看到了预览，但是mp4文件是空的，它根本没有保存视频到文件中。我想做的是使用directshow将视频流保存为mp4文件。现在我所能看到的就是在pictureBox中预览视频