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Old 20th February 2012, 09:30   #1  |  Link
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Navigation to the 1st frame: A problem in GraphEdit, a solution in MPC-HC?

Hello everyone,

I encountered a weird problem: I created a media file where each frame shows me its number. The problem is, my first frame isn't being displayed when I use GraphEdit to play it. If I use the File Writer to create a new file, instead of a renderer, then all frames are stored properly and the 1st one isn't left out. They just aren't displayed by the renderer. Interestingly, if I use both a renderer and the file writer, then the file writer skips the first frame as well.

MPC, however, is able to show me all frames and this is why I am posting here, in the hope of finding experts who know what MPC does to solve this problem.

Actually I found out about that problem while trying to create my own player in WinForms (C#) and the DirectShow.NET library. I use the Callback Events of the SampleGrabber filter to tell me the exact position in the video while I play it and I noticed that I don't get a Callback Event for the 1st frame. Also if I set the position to 0 using the IMediaSeeking interface, my player just navigates to the 2nd frame.

The formats of my test videos are RGB24 or RGB32 - both in Raw. They're 100x100 pixels, but I don't think it's because of an exotic resolution, because I also tried it with a 1280x800 raw RGB24 file and I had the same result.

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Old 22nd February 2012, 10:26   #2  |  Link
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After some testing, I can give more details to the problem:
Whenever I navigate to the 1st Frame in MPC-HC (no matter whether I use stop, the trackbar or step), I have to step forward twice to get to the 2nd Frame. After that, each step brings me to the next frame, just as it should. This looks like a bug at first sight, but I saw in an older version of MPC (release_v1_5_1_2903) that rewinding to the beginning (e.g. by clicking stop) didn't display frame 0, so I am guessing you used some kind of workaround to display that frame and this is why you have to step twice to get to the 2nd Frame. But now in the newer version the rewind-problem was solved and the workaround is still in there somewhere.

Like I said, I just guessed all that. Can anyone enlighten me, whether I am correct? Or maybe for a start you can just tell me which function is called when the stop-Button is pressed, because I can only find functions that return E_NOTIMPL.

There's something else I found out:
When we used a custom source filter in debug mode, we noticed that whenever we hit "stop" in MPC-HC, his stop-function and his seek-function are being balled twice (alternating). While doing that in my app didn't help, it still looks like a clue and I am going to follow any of those.
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frame, mpc-hc, navigation, seek

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