Error “Transparency encoding with auto_alt_ref does not work” when converting a .mov with Alpha to .webm with alpha with ffmpeg

Question

I am trying to convert a .mov file with alpha transparency into a .webm file and have been following this thread for help: Convert mov with Alpha to VP9 Webm with Alpha Using ff

Answer 1

I think I may have solved this, adding -auto-alt-ref 0 before the output fixed this issue!!

Working Command

ffmpeg -i Desktop/Skel_Walk_1.mov -c:v libvpx -pix_fmt yuva420p -auto-alt-ref 0 Desktop/Skel_Walk_1.webm