M4B is an audio filename extension for AAC format, which is developed by Apple Inc. It is mainly used on podcast and audiobook files. Typically, M4B files contain audio and other metadata like images, hyperlinks, and chapter markers. M4B files are DRM copy-protected and can be opened on Apple iTunes and QuickTime Player.
WebM is an open-source, royalty-free multimedia format for streaming content online. It contains compressed video streams of either VP8 or VP9 codec and compressed audio streams of Oupus or Vorbis codec. Today, it’s one of the most widely used file formats to stream videos online because of its lightweight and real-time delivery nature.
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