Publish will only accept MP3 files. Beyond this we have no requirements for specs- but we do have recommendations.
Since listeners download these files to their devices, you’ll want to strike a balance between audio quality and size. We recommend using files with a bit rate between 64 kbps- 128 kbps.
Most importantly, all the files you upload must have the same specs. Make sure that each segment has the same bitrate, sample rate, and loudness settings. (This also applies to any ad audio files you send to our advertising operations team).