MP4 is an extension defined by MPEG-4 video standard and AAC audio standard. It is a container that supports all kinds of media such as video, audio, subtitles, 2D and 3D graphics. It is possible to open MP4 file with almost any player on Windows but on Mac you should use a plug-in or just convert the file to another format.

WebM is an open media container compressed with VP8 video codec and Vorbis audio codec. WebM format has high video playback quality and data compression parameters.The format is widely used for adding media to web pages and it is supported by all modern web-browsers like Opera, Mozilla Firefox and Google Chrome. The embedding of WebM videos to a site page realizes without delays and errors. WebM is meant to be an alternative to the h.264 standard. The copyright of the extension is held by Google.