C# 如何知道一个影像文件能够播放多长时间

using DirectShowLib;

using DirectShowLib.DES;

using System.Runtime.InteropServices;

var mediaDet = (IMediaDet)new MediaDet();

DsError.ThrowExceptionForHR(mediaDet.put_Filename(FileName));

// find the video stream in the file

int index;

var type = Guid.Empty;

for (index = 0; index < 1000 && type != MediaType.Video; index++)

{

mediaDet.put_CurrentStream(index);

mediaDet.get_StreamType(out type);

}

// retrieve some measurements from the video

double frameRate;

mediaDet.get_FrameRate(out frameRate);

var mediaType = new AMMediaType();

mediaDet.get_StreamMediaType(mediaType);

var videoInfo = (VideoInfoHeader)Marshal.PtrToStructure(mediaType.formatPtr, typeof(VideoInfoHeader));

DsUtils.FreeAMMediaType(mediaType);

var width = videoInfo.BmiHeader.Width;

var height = videoInfo.BmiHeader.Height;

double mediaLength;

mediaDet.get_StreamLength(out mediaLength);

var frameCount = (int)(frameRate * mediaLength);

var duration = frameCount / frameRate;