Audio Encoding Guidance
Note on File Formats
At Castos, you can publish with the following file formats:
- Audio: .mp3, .aac, and .m4a
- Video: .mp4
The audio that you upload to our platform should be the same format and bitrate that your audience listens to. Castos does not perform any post-processing on your files.
File Export Settings
The export settings that we recommend for all of your audio files are:
- File Formats: MP3, AAC, M4A
- Bitrate:128 kbps
- Mono or Stereo: Mono is usually sufficient if it's just spoken word, but if you have sound effects then Stereo is a nice touch.
The bitrate that you export your files at is a balance between creating a really high fidelity file with a file size that's reasonable for your audience to download or stream. The highest fidelity file may have a slight increase in quality of sound, but will take too long for your audience to download. If the file is smaller it will download more quickly but will sacrifice a bit of audio quality along the way. The 128 kbps bitrate is a nice compromise between those two concerns.
Here's just a few other additional settings you may find in your audio editing software:
- Sample Rate: 44.1 kHz
- Bit Depth: 32-bit float or 24-bit
- mp3 Type: Constant Bit Rate (CBR)
What about loudness?
If you've ever switched from one podcast to another and noticed that one was waaaaay louder than the next then you've encountered inconsistent loudness settings. Loudness is the volume at which your files are exported, and should be benchmarked against these industry standards:
- Mono: -19 LUFS (this is the same perceived loudness as -16 LUFS for stereo)
- Stereo: -16 LUFS
Following the guidance above will give your podcast a high quality sound that your listeners will appreciate and keep them coming back.