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POSeeking keyframes using DirectShowNet
 

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  1. POSeeking keyframes using DirectShowNet
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    <p>My task is : I create a graph, attach a SampleGrabber to it, and grab the keyframes using the IMediaSeeking interface after building the graph.</p> <p>The following is what I have done : In the Main method :</p> <pre><code> Type comType = Type.GetTypeFromCLSID ( new Guid ( "e436ebb3-524f-11ce-9f53-0020af0ba770" ) ); IGraphBuilder graphBuilder = (IGraphBuilder) Activator.CreateInstance ( comType ); comType = Type.GetTypeFromCLSID ( new Guid ( "C1F400A0-3F08-11d3-9F0B-006008039E37" ) ); ISampleGrabber sampleGrabber = (ISampleGrabber) Activator.CreateInstance ( comType ); graphBuilder.AddFilter ( (IBaseFilter) sampleGrabber, "samplegrabber" ); AMMediaType mediaType = new AMMediaType ( ); mediaType.majorType = MediaType.Video; mediaType.subType = MediaSubType.RGB24; mediaType.formatType = FormatType.VideoInfo; sampleGrabber.SetMediaType ( mediaType ); int hr = graphBuilder.RenderFile ( @"D:\test.wmv", null ); IMediaEventEx mediaEvent = (IMediaEventEx) graphBuilder; IMediaControl mediaControl = (IMediaControl) graphBuilder; IVideoWindow videoWindow = (IVideoWindow) graphBuilder; IBasicAudio basicAudio = (IBasicAudio) graphBuilder; videoWindow.put_AutoShow ( OABool.False ); basicAudio.put_Volume ( -10000 ); sampleGrabber.SetOneShot ( false ); sampleGrabber.SetBufferSamples ( true ); //the same object has implemented the ISampleGrabberCB interface. //0 sets the callback to the ISampleGrabberCB::SampleCB() method. sampleGrabber.SetCallback (this, 0); mediaControl.Run ( ); EventCode eventCode; mediaEvent.WaitForCompletion ( -1, out eventCode ); Marshal.ReleaseComObject ( sampleGrabber ); Marshal.ReleaseComObject ( graphBuilder ); </code></pre> <p>In the SampleCB() callback method :</p> <pre><code> public int SampleCB ( double sampleTime, IMediaSample mediaSample ) { Console.WriteLine ( "SampleCB Callback" ); Console.WriteLine ( mediaSample.IsSyncPoint ( ) + " " + mediaSample.GetActualDataLength() ); //check if its a keyframe using mediaSample.IsSyncPoint() //and convert the buffer into image and save it. return 0; } </code></pre> <p>Thus, I have set up the things. Now, when i run the program, everything loads correctly. But the callback is called only once, and then the rendering stops. No more rendering and no more callbacks. I had tried the another callback method ISampleGrabber::BufferCB() to see if it follows the same fate. But no! BufferCB() is called everytime a frame is grabbed and the video is rendered till the end.</p> <p>What am I doing wrong? Any suggestions on this? Thank you :)</p>
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    1. USJayesh Bhoot
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