I’m trying out for my school talent show tomorrow by showing a speedpaint. I’m on a Mac, so of course all my editing will be done on free-to-use shitty programs. OBS decided to save the first three hours of work as a .flv instead of a .mp4, which would be fine but iMovie doesn’t like to work with .flv.
I’ve been trying to use VLC to convert it to a .mp4, but throughout all three hours of the converted video it’s just the first still frame. The whole recording is shown in the .flv. Help?

VLC will be a problem. Maybe try Wondershare? It's the second one listed if you follow this link: http://www.techisky.com/software/avs-video-converter-for-mac.html

Thank you for the help, however the application requires me to pay in order to convert more than 1/3 of the video. :(

Oh, that's useless. You could try cloudconvert.com. It's cloud based and platform independent.
Or I think this one is free, but I haven't used it before: https://itunes.apple.com/us/app/free-mp4-converter/id693443591?mt=12
Good luck!