Daily UI- Ecomm Messages and Notifications

Day 4 of developing a UI kit for an ecomm app. I have been trying to figure out how to convert recorded xd prototype videos into gifs with a static 1600x1200 background. Has anyone done this before? What tools do you use to convert? I tried the Adobe encoder for gif videos and it works great but doesn't let me add a 1600x1200 static/colored background? Wondering if there is a way to do this?