Does Castos alter media files after they're uploaded?

No. We believe the file that you upload should be exactly the same file that your audience listens to. We don't modify the metadata, bitrate, or file format of your podcast files when (or after) they're uploaded to our platform.

Generally though, we do recommend you use the .mp3 file format and at a bitrate of 128kbps as that's a nice middle ground between high fidelity and reasonable file size for most spoken audio.