The file extension stands for MPEG-4 Audio Book . It is very similar to the more common .m4a format but has specific features optimized for long-form audio:
Valya’s own training under the brutal Reverend Mother Raquella Berto-Anirul. We witness the agony of the Agony —the spice poison ritual that unlocks ancestral memory—and the revelation that the Sisterhood’s long goal (the Kwisatz Haderach) was born from a lie Valya planted to unify the scattered schools. dune: prophecy s01e01 m4b
In the aftermath of the Butlerian Jihad—a crusade against thinking machines that reshaped the Imperium—the fledgling Bene Gesserit sisterhood operates in shadow, long before the rise of Paul Atreides. Episode 1, “The Hidden Hand,” opens on Wallach IX, the secretive training world of the Sisterhood. The file extension stands for MPEG-4 Audio Book