Read this page, see if it has any info that helps.... It does talk about Webm and transparency a bit...  Most-current info on the Help Center,   <a href="https://help.roll20.net/hc/en-us/articles/360037256634-Best-Practices-for-Files-on-Roll20" rel="nofollow">https://help.roll20.net/hc/en-us/articles/360037256634-Best-Practices-for-Files-on-Roll20</a>   Outdated version on the Wiki,    <a href="https://wiki.roll20.net/Image_Best_Practices_for_Roll20" rel="nofollow">https://wiki.roll20.net/Image_Best_Practices_for_Roll20</a>   Ultimately if the answer is not there, it probably should be, so if you find out... let's try to get it added to Help Center.  Webm itself is a relatively newer format that has recently been gaining traction, which is maybe a reason information is sparse.   Webm is a format invented by Google, so IDK if any Google apps exist for animations editing