At least since July 2012 for 3dscapture.com I guess since that's when their software came out. It's handled by more than one company as well. Here's another company that does it as well - http://www.3dsvideocapture.com/product/27 and they do it for 3ds xl as well :). Theres lots of things out there we don't know of…

So more along the lines of what you really needs is a 3DS Capture? http://3dscapture.com/ <- 3ds capture board that gets installed into your 3ds and lets you output video via USB. This way it'll pretend to be a PC game ;) and it'll just be more games on the same screen! haha