How do people record their handheld consoles?

[jasonsl8five]

I've been on youtube and seen some walkthroughs of ds games like phantom hourglass and I've been wondering how do they record their ds's. It's not an emulator if that's what you're thinking because it works perfectly. I'm positive they don't use emulators so how do they record their ds. I mean, it fits the screen. Like this is what I mean, how do they record their ds's.
http://www.youtube.com/watch?v=bldbc6UFDkA