关于directshow 播放视频的问题

syj8905760 2008-04-26 10:53:30

我想用ISampleGrabber来将avi视频中截图。代码如下。但现在的问题是，为什么在播放avi视频时，只有图像，没有声音出来。哪位高手指点一下啊

        

private void SetupGraph(Control hWin, string FileName)

        {

            int hr;



            // Get the graphbuilder object

            m_graphBuilder = new FilterGraph() as IFilterGraph2;



            // Get a ICaptureGraphBuilder2 to help build the graph

            ICaptureGraphBuilder2 icgb2 = new CaptureGraphBuilder2() as ICaptureGraphBuilder2;



            try

            {

                // Link the ICaptureGraphBuilder2 to the IFilterGraph2

                hr = icgb2.SetFiltergraph(m_graphBuilder);

                DsError.ThrowExceptionForHR( hr );



#if DEBUG

                // Allows you to view the graph with GraphEdit File/Connect

                m_DsRot = new DsROTEntry(m_graphBuilder);

#endif

                // Add the filters necessary to render the file.  This function will

                // work with a number of different file types.

                IBaseFilter	sourceFilter = null;

                hr = m_graphBuilder.AddSourceFilter(FileName, FileName, out sourceFilter);

                DsError.ThrowExceptionForHR( hr );



                // Get the SampleGrabber interface

                m_sampGrabber = (ISampleGrabber) new SampleGrabber();

                IBaseFilter baseGrabFlt = (IBaseFilter)	m_sampGrabber;



                // Configure the Sample Grabber

                ConfigureSampleGrabber(m_sampGrabber);



                // Add it to the filter

                hr = m_graphBuilder.AddFilter( baseGrabFlt, "Ds.NET Grabber" );

                DsError.ThrowExceptionForHR( hr );



                // Connect the pieces together, use the default renderer

                hr = icgb2.RenderStream(null, null, sourceFilter, baseGrabFlt, null);

                DsError.ThrowExceptionForHR( hr );



                // Now that the graph is built, read the dimensions of the bitmaps we'll be getting

                SaveSizeInfo(m_sampGrabber);



                // Configure the Video Window

                IVideoWindow videoWindow = m_graphBuilder as IVideoWindow;

                ConfigureVideoWindow(videoWindow, hWin);



                // Grab some other interfaces

                m_mediaEvent = m_graphBuilder as IMediaEvent;

                m_mediaCtrl = m_graphBuilder as IMediaControl;

            }

            finally

            {

                if (icgb2 != null)

                {

                    Marshal.ReleaseComObject(icgb2);

                    icgb2 = null;

                }

            }

#if DEBUG

            // Double check to make sure we aren't releasing something

            // important.

            GC.Collect();

            GC.WaitForPendingFinalizers();

#endif

        }