WebM initially supported VP8 video and Vorbis audio streams. The WebM container is based on a profile of Matroska. The original video compression format used in the file, also known as WMV, was originally designed for Internet streaming applications compared to RealVideo. Windows Media Video (WMV) is a file type that can contain video in several video compression formats developed by Microsoft.
Google sponsors the development of the format, and the corresponding software is distributed under a BSD license.
It has a sister project, WebP, for images. It is primarily intended to offer a royalty-free alternative to use in the HTML5 video tag.