WMA (Windows Media Audio) is a collection of multiple sound codecs and their respective coding formats. It was developed by Microsoft in 1999 as part of its Windows Media framework. WMA features up to four codecs, including WMA, WMA Pro, WMA Lossless, and WMA Voice. Each codec has its own distinct function.
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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.