This may be a stupid question but is your video cable plugged into the gpu or into the motherboard?

In your case I would just start by copying a full setup someone else made and then customizing it, starting from scratch always takes a lot of effort. Reddit’s unixporn was great for that, the alternatives on lemmy are sadly still a little empty.

ffmpeg can do this easily, but I don’t have a full command for you right now

bash’s autocomplete fails (at least with default settings), but e.g. zsh can figure out what you mean