"The ESV Hear the Word Audio Bible MP3 format comes as 8 zip download files, containing a folder for each book of the Bible and 1 MP3 file for each chapter. The M4B format comes as 8 zip download files, containing 1 M4B file for each book (bookmarked & navigable by chapter)."
For those who don't know what an M4B file is, it is an audio file that may be played on iTunes. I think Windows Media Player might also play this kind of file. For more information see here.