WEBM as maps background - supported and working or not?

Hello - I have done a fair bit of looking around and I cannot find any instance where some has a recipe that says - do this and webm works.  I have tried a few different ways, the upload either dies, or finishes and I cannot add it to a page., the only support statement I found says it should work?  If there is anything definitive known out there, it would be great so I stop trying. if it's a hard "no" .  The file is less than 5 MB so it's not a file size thing.  Thanks

My experience it works for animated tokens, some animated effects like rain or smoke. For animated maps it has never work for me no matter the size.

What is the source of your animated maps? While all files of a given file type are supposed to all be the same that is not always the case, there can be quirks based on the creation program.  If an image is not uploading to Roll20 one trick that *sometimes* works is to edit/resave the image in a different program than the one that created it.  Something to also remember is that uploading to Roll20 isn't actually just uploading, it is also Roll20 reprocessing the image.  Finally, if an image is not uploading correctly I suggest filing a bug report in the Help Center and sending the image to Roll20 to investigate. Maybe they can get enough data about what kinds of images are giving them issues to work on it.