Anyway it seems it doesn't have a VideoDetect function, it's a DriverDetect function, since it's used for sound too.
First it goes through the video drivers in the following order:
VGA, TGA, EGA, HGA, HERC, and CGA.
Then it goes into the audio drivers:
stdsnd, adlib, covox, gblast, ibmg, sblast, tandy.