After many delays, much hemming, and lots of hawing, the ability to play WebM video (vp9/opus) was merged into the main codebase today. You should still be able to compile the new codebase after this merge; however, if you would like to be able to see videos in the client, you will need to download the new devlibs bundle.
There are currently no official WebM versions of the Cyan introduction video nor the MOUL intro video. For now, you will need to convert them using third party utilities if you want them to play. We hope to fix this in the near future.