FFMPEG: Video format replacement for webm (alpha channel)

Question

I am currently creating a webm file using two mp4's (alpha - black background, white silthoette) and normal video.

Using following ffmpeg command:

ffmpeg -i color.mp4 -i alpha.mp4 \
       -filter_complex [0][1]alphamerge,format=yuva420p \
       -c:v libvpx -strict -2 -auto-alt-ref 0 \
       output.webm

And while this works fine for most browsers, it doesn't work on iOS, so I need to create a .mov (or maybe something else?) file with transparent background.

What is the proper way to do it in ffmpeg?

Answer 1

Can you try using the following:

ffmpeg -hide_banner -y -i color.mp4 -i alpha.mp4 \
   -shortest -filter_complex [0:v][1:v]alphamerge -map \
   0:a:0 output.webm