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.
AC3 is an audio format designed by Dolby Digital to offer surround sound listening. This format is available on most Blu-ray and DVD media files and is played using a Dolby Digital DVD Player. Interestingly, AC3 can be output in up to six speakers of a home stereo system. On a computer, AC3 can be opened on VLC Media Player, Apple QuickTime Player, and Windows Media Player.
VLC Media Player Apple QuickTime Player Windows Media Player