如何获取媒体长度（播放时间............. 急...........）(40分)

我是用DirectShow做播放器，在获取媒体长度时，老是报错！
搞不懂，晕........................
function TVideoPlayer.GetVideoPlayTime(const FileName: PWideChar): int64;
var
VideoLongth: int64;
Graph: IGraphBuilder;
MediaSeeking: IMediaSeeking;
begin

try
// CoInitialize(nil);
CoCreateInstance(CLSID_FilterGraph, nil, CLSCTX_INPROC_SERVER,
IID_IGraphBuilder, Graph);
Graph.RenderFile(FileName, nil);
Graph.QueryInterface(IID_IMediaSeeking, MediaSeeking);
//获取媒体总时间
MediaSeeking.SetTimeFormat(TIME_FORMAT_MEDIA_TIME);
MediaSeeking.GetDuration(VideoLongth);
Result := VideoLongth;
finally
Graph := nil;
MediaSeeking := nil;
//CoUninitialize;
end;

//Result := 100000000;
end;

看看这对你有没有帮助！
function GetAviLength(Alength: integer):string;
var
alltime: LongInt;
minutes, seconds: integer;
begin

MediaPlayer1.TimeFormat := tfmilliseconds;
alltime := Alength;
minutes := alltime div 60000;
seconds := (alltime - 60000 * minutes) div 1000;
Result:=inttostr(minutes) + '分' + inttostr(seconds) + '秒';
end;


长度:=GetAviLength(MEDIAPLAYER1.LENGTH);

问题自己解决，还是要谢谢 “清新空气”！
给分了哦！