Publish will only accept MP3 files. Beyond this we have no requirements for specs- but we do have recommendations.
- Use a bitrate between 64 kbps-128 kbps
- Since listeners download these files to their devices, you’ll want to strike a balance between audio quality and size.
- Set your loudness between -16db LUFs and -19db LUFs. There is no set industry standard, but this range was agreed upon by the fine and knowledgeable folks of PRX.
- Be consistent with all file 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).
- Add ID3v2 tags to your first segment.
- With ID3v2 the headers are located at the start of the podcast (not at the end). This allows players to use the ID3 data (title, artist, etc) ahead of streaming time without downloading the full podcast file. You can add and edit ID3v2 tags through iTunes or some digital audio workstations.
- Limit ID3 tag size to 300kb with 800x800 pixels max for the artwork.