As its title may suggest, an MP3 player's primary duty is to play MP3s, which are more often than not music files. But audiobooks, podcasts, and other spoken-word content enjoy plenty of face time on portable audio devices, and why not? They offer an informative and entertaining way to pass the time. But for those of us who prefer our information and entertainment in condensed form, time is of the essence. Spoken-word content is one type of audio that (generally) doesn't sound completely absurd when sped up, and doing so gives the listener a way to get through said files with due haste.
Luckily, there are a handful of MP3 players on the market that offer a feature known as variable playback speed, which allows you to speed up (or slow down) audio on-the-fly--no clunky software conversions required.