Creating a custom render profile and trying to figure out what "g=120" means on some of the preset profiles.

see ffmpeg doc: it is the "Group of Pictures" (gop) size, max number of frames between 2 I-frames (full image).
DVD used to have g=12, for higher compression some recorders use very long gops, but it makes seeking very difficult.
youtube asks for max g=15 or so...

Thank you for the answer. I will dig into this a bit deeper but at least I have a direction to head in now!