You should record audio at the best quality you can manage, using a lossless file format (like .wav). However, the files will have to be processed for sharing to be lighter.
When it comes to sharing your audio as a podcast, MP3 and M4A files are the only audio filetypes that are supported for podcast apps (like Apple Podcasts). Acast supports both file formats.
We recommend uploading mp3 files with a bitrate of 128kbps. These typically have the right balance of good audio quality and small size, which your listeners and apps will appreciate.
Acast will encode your uploaded files at 128kbps, which will not impair the perceived quality for your listeners.
If you have recorded in a different file format (like .wma) use your audio editing software (such as Garageband or Audacity) to export the episode audio file as MP3 or M4A as recommended above.
What are the limits?
Most people use the Apple Podcasts app to listen to podcasts. Apple has set the file limit to 150MB for all files downloaded over a cellular connection (including apps, ebooks, and videos).
When your listeners try to play your episode, they are greeted with a pretty unhelpful message—"episode unavailable"—which is a frustrating experience to say the lease. To help our podcasters avoid this issue, Acast sets the internal limit to 150MB also.
To make your file smaller, use your audio editing software (like Garageband or Audacity) to export the episode audio file at a lower bitrate. Choose to export at 128kbps MP3.