AWS Elemental MediaConvert now offers expanded support for audio-only workflows with the ability to create MP3 audio files. With MediaConvert, you can easily produce MP3 audio for devices and services that use this format with a simple selection from the console. Create MP3 files in standalone audio conversion jobs, extracted from video files, or as supplementary outputs produced during the video transcoding process. To learn more about supported audio formats, please see the documentation pages.

from Recent Announcements: https://aws.amazon.com/about-aws/whats-new/2020/01/mp3-audio-output-now-available-with-aws-elemental-mediaconvert/