If it’s twice as wide as you want, just resize it. More important is that you probably ending up with both planes, left and right being identical, meaning it will not have 3D effect. Just tested it myself with latest version of ffmpeg. Still no official MVC support it seems…
There’s no point in trying to use Meta-crap “privately”, as these services main goal is to NOT respect privacy and make life miserable for anyone who dares. If you really need it for work-releated stuff, buy a second phone/device, register another e-mail - basically create separate digital identity for your “public” (non-private) life. Otherwise you will have to deal with various annoyances, like randomly logging you out, demanding SMS authentication or locking your account for some dumb reasons. Insta/FB are absolute garbage, and the last thing we should give them is our anger and stress due to dealing with their BS. It’s not good for your health folks :)