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| Name | M4B | AAC |
| Full name | MPEG-4 Audio Layer Bookmarkable File | AAC - Advanced Audio Coding |
| File extension | .m4b | .aac |
| MIME type | audio/m4b | audio/aac |
| Developed by | Apple | Bell Labs, Fraunhofer Institute etc. |
| Type of format | Music File | Audio compression format |
| Description | Audiobook and podcast files which also contain metadata including chapter markers, images, and hyperlinks can use the extension .m4a but more commonly use the .m4b extension. M4b files support metadata for chapters and bookmarking on supporting players and most commonly uses AAC (Advanced Audio Codec). | Advanced Audio Coding (AAC) is an audio coding standard for lossy digital audio compression. Designed to be the successor of the MP3 format, AAC generally achieves better sound quality than MP3 at similar bit rates. AAC has been standardized by ISO and IEC, as part of the MPEG-2 and MPEG-4 specifications. |
| Technical details | The audio in a M4b file is encoded with the AAC compression format and can therefore be protected with Apple's FairPlay DRM copy protection system. M4b files can contain metadata as defined by the format standard and in addition can contain Extensible Metadata Platform (XMP) metadata. | AAC supports inclusion of 48 full-bandwidth audio channels in one stream plus 16 low frequency effects channels, up to 16 "coupling" or dialog channels, and up to 16 data streams. The quality for stereo is satisfactory to modest requirements at 96 kbit/s in joint stereo mode; however, hi-fi transparency demands data rates of at least 128 kbit/s. |
| Associated programs | Apple QuickTime Player, Apple iTunes | foobar2000, AIMP, DirectShow, QuickTime, VLC media player. |
| Wiki | https://en.wikipedia.org/wiki/MPEG-4_Part_14 | https://en.wikipedia.org/wiki/Advanced_Audio_Coding |