MPEG-4 for audio (M4B)

M4A and M4B are audio file formats and file extensions (*.m4a, *.m4b) in MP4 containers. The letter "a" stands for audio streaming, "b" for audiobooks.

The audio files within the MP4 container, which is created in the MP4 file format, can in principle be encoded with any audio codec, but Advanced Audio Coding( AAC) is mostly used to pack the audio files into the MPEG container.

Both audio file formats are essentially identical except for the difference that M4A is used in Apple`s Music Store iTunes and the iPod and iPad recognize M4B data files as audio books and allow bookmarking.

Audio books in M4B format can be burned up to seven times on a compact disc, copied as many times as needed on an iPod and listened to on up to five computers. M4B files cannot be converted to MP3.

The extensions for the audio files have the suffixes *.m4a and *.m4b and are used by various programs such as Quicktime or ACDSee.