The video will show you how to make a square border inside of davinci resolve 16
If you have any questions I am always happy to answer them in the description or on discord.
Link to the website https://ffmpeg.org/
ffmpeg -i FileName00000000.mov -c:v libvpx-vp9 -pix_fmt yuva420p Endname.webm
Do not put spaces or it might not work