macOS can play an MP3 but has no way to make one. WAV and M4A are written by macOS itself; MP3 is the one format that needs an encoder from outside — and the encoder everyone uses is LAME, a free library and command-line tool that has been the reference MP3 encoder for more than twenty years.
The short version
Pro: nothing to install
Podcast Track Cleaner Pro carries its own copy of LAME inside the app. Download the app, choose MP3 in the export sheet, done. This page is for when you want to check which encoder is in use, or use a different one.
Mac App Store edition: export M4A
A sandboxed App Store app isn't allowed to ship LAME under its licence or run a copy from your Mac, so that edition is built without MP3 at all. Export M4A (AAC) instead: it is smaller than MP3 at the same quality and every podcast host and player takes it. If you need MP3 itself, use Pro — the two editions open the same projects.
Check what's in use
Open Settings ▸ Encoders (⌘,). The box at the top shows the LAME version and the path it runs from:
| Path shown | Meaning |
|---|---|
…/Podcast Track Cleaner Pro.app/Contents/Helpers/lame | The copy built into the app — the normal case |
/opt/homebrew/bin/lame or /usr/local/bin/lame | A copy installed with Homebrew |
| Any other path | A copy you chose with Choose… |
| Not installed | No encoder found; MP3 export is unavailable until there is one |
Check Again looks once more — after you've installed or moved a copy, for instance. The export sheet says so too when MP3 has no encoder, and points you here.
Which copy wins
When it exports, the app looks for an encoder in this order and uses the first that runs:
The one you chose
A path set with Choose… in Settings ▸ Encoders. Reset Path forgets it.
The one inside the app
Pro's own copy, in the app bundle.
One installed on the Mac
/opt/homebrew/bin/lame(Homebrew on Apple silicon),/usr/local/bin/lame(Homebrew on Intel, or built by hand),/opt/local/bin/lame(MacPorts),/usr/bin/lame.
Using your own LAME
You don't need to — the built-in copy is current and unmodified. But if you'd rather run a build you control, or you are running Track Cleaner built from source, which has no bundled copy:
With Homebrew
If Homebrew is installed and the app has no encoder of its own, Settings ▸ Encoders shows an Install with Homebrew button: it runs brew install lame and shows the output as it goes. No administrator password is involved; Homebrew installs into its own folder. Or run it yourself in Terminal:
brew install lamethen press Check Again. Note that the copy inside the app still comes first; to prefer the Homebrew one, point at it with Choose….
Any other copy
Press Choose… and pick the lame executable — the dialog shows hidden folders, so /usr/local/bin and the like are reachable. Anything that accepts LAME's command-line options will work. Reset Path goes back to the built-in copy.
Export settings
In the export sheet (⌘E), MP3 offers a constant bitrate — 128, 192, 256 or 320 kbps — or, with VBR ticked, a quality level from V0 (best) to V4 (smallest). For speech, 128 kbps mono or V4 is plenty and keeps the download small; music-heavy shows may want more. The default for new exports — constant or variable — is in Settings ▸ Editing. Tags and chapters are written into the MP3 after encoding; see ID3 tags.
About the licence
LAME is free software under the GNU Lesser General Public License. Pro bundles LAME 4.0, unmodified, built from the official source with its MP3 decoder left out, so no GPL code is included. The app never links against it: it writes a temporary WAV and runs lame as a separate program, which keeps LAME's licence with LAME. The licence text and the exact source the copy was built from travel inside the app, in Contents/Resources (right-click the app ▸ Show Package Contents).