I am trying to convert a mov with alpha transparency to webm with alpha transparency, as seen here. I followed the steps explained here to
All of the other solutions resulted in a video of subpar quality. Please ensure that you define the bitrate to your liking. I changed mine from 1M to 2M and was satisfied.
ffmpeg -i "Model 1 V1.mov" -f webm -c:v libvpx -b:v 2M -acodec libvorbis -auto-alt-ref 0 model1v3.webm -hide_banner
If you're using After Effects or Premiere Pro, there's also this plugin, which can be used in Adobe Media Encoder.