From what I understand, the current version of Mednafen supports WonderSwan TASing on a Windows system? At least according to adelikat's last post regarding the issue. I'm using the front loader and everything works like a dream, except for actual recording. I can run any WonderSwan game just fine, configuring hotkeys and my inputs was no problem, nor is loading from an existing savestate (not that I'd use this option to begin a recording, but I tested it just for clarity's sake). However, trying to initiate a recording while a ROM is running doesn't register at all, and playback just resets the console and tells me playback has stopped.
Checking off the 'record movie' box before Mednafen starts up results in a 'recording' and "recording has started" text showing up as the ROM boots, but the ROM is frozen at the first frame. I can even save and load a state from this frame. This is basically the only thing about the emulator that causes any trouble at all, and for the life of me I can't figure out what's causing it to freeze this way. It's purely the ROM itself that freezes, too. The emulator runs just fine as this is happening. It's not causing anything to crash.
EDIT: Nevermind, I figured it out. Good lord I'm dense.