I wanna record top screen ONLY, because:
1. Bottom screen is not necessary to show
2. If I don't record bottom screen, desmume can running faster.
Someone can help me? My computer is too slow
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See http://wiki.desmume.org/index.php?title=Faq#How_can_I_record_an_AVI_with_a_gap_between_the_screens.3F

I already tried this. But I fail at the part "Compiling".
I really don't know what program I have to use to do it.
Visual Studio 2010 Express doesn't work with it.

DON'T EVER USE VS 2010 ON DESMUME!!!
That's something I leanred after trying it. I wasted so much time.

I thought there was an option to only display the top screen... I must have been mistaken.

Anyways, it's not like the resulting video is slow. It'll be at full speed (like on a DS).

And I had another thread on this board somewhere where I had some ffmpeg options to crop out the bottom screen of recordings from DeSmuME.

Yes, desmume *can* be compiled on VS2010.

Look at the last post in http://forums.desmume.org/viewtopic.php?id=2949.