使用DirectShowNet寻找关键帧 [英] Seeking keyframes using DirectShowNet

问题描述

我的任务是:创建一个图形，将SampleGrabber附加到该图形上，并在构建图形后使用IMediaSeeking界面获取关键帧.

My task is : I create a graph, attach a SampleGrabber to it, and grab the keyframes using the IMediaSeeking interface after building the graph.

以下是我所做的: 在Main方法中:

The following is what I have done : In the Main method :

   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 );

在SampleCB()回调方法中:

In the SampleCB() callback method :

    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;
    }

因此，我已经完成了设置.现在，当我运行程序时，一切都正确加载.但是回调仅被调用一次，然后呈现停止.没有更多的渲染，也没有更多的回调. 我尝试了另一个回调方法ISampleGrabber :: BufferCB()来查看它是否遵循相同的命运.但不是！每次抓取一帧并将视频渲染到最后时，都会调用BufferCB().

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.

我做错了什么?有什么建议吗? 谢谢:)

What am I doing wrong? Any suggestions on this? Thank you :)

推荐答案

好..我终于能够解决该问题.我会在这里描述它，以防它对其他人有帮助. 我实际上并没有在回调方法中释放IMediaSample对象.这是必须要做的，因为它是一个COM对象.

ok..I have finally been able to solve that problem. I would describe it here in case it helps anyone else. I was not actually releasing the IMediaSample object in the callback method. That is a must to do, it being a COM object.

只需将Marshal.ReleaseComObject()添加到我的SampleCB()回调方法中，现在每次SampleGrabber抓取一个样本时都会调用它.

On simply adding the Marshal.ReleaseComObject() to my SampleCB() callback method, it is now called everytime the SampleGrabber grabs a sample.

public int SampleCB ( double sampleTime, IMediaSample mediaSample )
{
    Console.WriteLine ( "SampleCB Callback" );
    Console.WriteLine ( mediaSample.IsSyncPoint ( ) + " " );

        /* other code */
    Marshal.ReleaseComObject ( mediaSample );
    return 0;
}

我现在面临另一个问题.但是，我为此发表了另一篇文章，因为它并不完全与此问题相关.

I am facing another issue now. However, I have made another post for that as it doesnt totally relate to this question.

这篇关于使用DirectShowNet寻找关键帧的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！