WTV (Windows Recorded TV Show File) is a video format recorded using Windows Media Center (WMC). WMC is a program for recording TV shows and playing multimedia content. WTV uses the MPEG-2 compression standard for videos and Dolby Digital AC-3 or MPEG-1 Layer II for audio. Some WTV files might include metadata as well as DRM protection.
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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.