Video ffmpeg .mov file with alpha to webm format

i want to convert a 6MB quicktime .mov file to webm and preserve the alpha. unity 2017 on windows is the target platform and i'm creating on windows 7 using unity 2017. i simply want to map the webm video to a plane using 'videoplayer'. i have converted a smaller version of the .mov using an online service and it worked nicely, but that site charges after the 100KB freebee, and they won't convert a file this large. i've also tried several other online vendorsas well as sites where you download their interface, and am no longer comfortable with that approach for a variety of reasons (one online site actually core dumped my very stable computer twice, and i didn't even download their software - very weird and scary). i realized i could do it myself for free with ffmpeg so that's my goal. i successfully did a ffmpeg command line conversion without the alpha channel of the 6 MB .mov file to webm and can play it back outside of unity, but it won't play back in unity. i notice unity does not transcode it like other files, and its icon looks like a page with the corner turned down. there's a lot of tricky documentation out there so if anyone can cut through the clutter for me that would be great - thanks

 

This Video Packer
And this FFmpeg Unity Bind
Could be interesting for you.

Cheers!

 

I use this and works fine (windows/Linux only):

https://sourceforge.net/projects/ffmpegyag/

 

in the end i used this plugin in premiere. i got it from github but it's also here:

http://www.fnordware.com/WebM/