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How to convert AIFF or WAV to MP3 on a Mac

Tested on macOS 26.4.1 (Tahoe), Apple M3 Max, 3 Sept 2026. Updated 2026-09-03.

You can convert a WAV or AIFF to MP3 on a Mac for free in three ways: the Music app (set Import Settings to MP3 Encoder, then File > Convert > Create MP3 Version), ffmpeg with libmp3lame, or lame itself. Apple's built-in afconvert cannot write MP3; the attempt fails with a format error. A 320 kbps MP3 is 2.4 MB per minute.

Can afconvert convert to MP3?

No. afconvert -hf on macOS 26.4.1 does list 'MPG3' = MPEG Layer 3 (.mp3) as a file format, which makes people try it, but that entry is for reading. Running afconvert -f MPG3 -d '.mp3' in.wav out.mp3 on this Mac returns:

Error: ExtAudioFileSetProperty ('cfmt') failed ('fmt?')

The ss64 man page states it plainly: "MacOS and afconvert do not include an MP3 encoder, though there is a MP4 (lossy) encoder. If you need to create MP3, use Lame or iTunes" (ss64, afconvert). The same applies to Finder's Encode Selected Audio Files quick action, which offers AAC and Apple Lossless only. If AAC in an .m4a is acceptable, it is one command and usually the better codec; see how to convert a Mac recording to M4A or AAC. If it must be MP3, use one of the three routes below.

How do I convert WAV to MP3 with the Music app?

Apple's documented route, no install needed (Apple, Convert music file formats):

  1. Open Music. Choose Music > Settings, click Files, then click Import Settings.
  2. In the Import Using pop-up menu choose MP3 Encoder, pick a quality, then click OK.
  3. Drag the WAV or AIFF into the Music window so it appears in your library.
  4. Select it and choose File > Convert > Create MP3 Version.

Apple notes that "the song in its original format and the newly converted song appear in your library", so the original stays. The downsides: the MP3 is written into the Music media folder, not next to your source; you must drag it back out; and the import step copies the WAV into the library unless you have turned that off. For one file it is fine. For a folder of DJ sets it is slower than a single Terminal command.

How do I convert with ffmpeg or LAME in Terminal?

Neither tool ships with macOS; install one with Homebrew (brew install ffmpeg or brew install lame). Then:

  1. Constant 320 kbps with ffmpeg: ffmpeg -i in.wav -c:a libmp3lame -b:a 320k out.mp3. The ffmpeg docs describe b as "Set bitrate expressed in bits/s for CBR or ABR" (ffmpeg codecs documentation).
  2. Variable bitrate with ffmpeg: ffmpeg -i in.wav -c:a libmp3lame -q:a 2 out.mp3, where q is "Set constant quality setting for VBR" and maps to LAME's -V.
  3. Constant 320 kbps with LAME directly: lame -b 320 in.wav out.mp3.
  4. Variable bitrate with LAME: lame -V 2 in.wav out.mp3. The LAME documentation gives the scale as 0 to 9, "0 is the highest quality while 9.999 is the lowest one", with -V0 averaging about 245 kbps and -V2 about 190 kbps (LAME usage).

To batch a folder: for f in *.wav; do ffmpeg -i "$f" -c:a libmp3lame -b:a 320k "${f%.wav}.mp3"; done. LAME reads WAV and AIFF; if a file is refused, convert it to 16-bit WAV first with afconvert -f WAVE -d LEI16.

Which MP3 bitrate should I use?

Size is set by the bitrate alone: bytes per minute = bitrate / 8 x 60. From the measured 2.4 MB per minute at 320 kbps, the arithmetic gives 1.9 MB per minute at 256 kbps, 1.4 MB per minute at LAME's -V2 average of 190 kbps, and 0.96 MB per minute at 128 kbps. A 2-hour set is 288 MB at 320 kbps.

Keep the WAV or AIFF master if you might edit later; encoding an MP3 from an MP3 loses quality each time, which Apple warns about for compressed-to-compressed conversion. The size trade-off across all formats is in how big is an audio recording per minute and the keep-or-delete decision in WAV vs AIFF vs MP3.

Select one or more songs in your library, then choose File > Convert > Create [format] Version.

Apple, Music User Guide for Mac

Ways to make an MP3 from a WAV or AIFF on a Mac

MethodPriceNeeds installExact bitrate controlBatch a folderWrites next to the sourceConverts existing files
afconvert (built in)0nonot applicableyesyesno, cannot write MP3
Music app, Create MP3 Version0nopreset choicesyes, multi-selectno, Music media folderyes
ffmpeg + libmp3lame0yes (Homebrew)yes, CBR or VBRyes, shell loopyesyes
LAME0yes (Homebrew)yes, CBR or VBRyes, shell loopyesyes
AirCheck export$39yes320 kbps CBR onlyno~/Music/AirCheckno, only the take it just recorded

Tested on macOS 26.4.1. Prices as of Sept 2026.

Where AirCheck fits

AirCheck ($39, macOS 14 or newer) is useful when you know before pressing record that you want an MP3: choose MP3 320 kbps as the export format and the app converts the 24-bit AIFF master with its bundled LAME helper the moment the take stops, at 2.4 MB per minute, into ~/Music/AirCheck. No Music library import, no Terminal. It converts only what it recorded; it is not a general file converter.

When you do not need it: For files you already have, the Music app is free and does the job, and ffmpeg is faster for a folder. Do not buy anything just to convert existing WAVs.

AirCheck records what your Mac plays, or any input, to one file. $39 once.

Buy AirCheck for $39

macOS 14 or newer. One-off payment. Fourteen-day refund, no questions asked.

Questions people ask

How do I convert WAV to MP3 on Mac for free?

Use the Music app: Music > Settings > Files > Import Settings, choose MP3 Encoder, then select the song and pick File > Convert > Create MP3 Version. Or install ffmpeg with Homebrew and run ffmpeg -i in.wav -c:a libmp3lame -b:a 320k out.mp3.

Why does afconvert fail with MP3?

Because macOS ships no MP3 encoder. afconvert lists MPG3 as a readable file type, but writing it returns ExtAudioFileSetProperty ('cfmt') failed ('fmt?'). Use LAME, ffmpeg or the Music app instead, or convert to AAC with afconvert.

Does converting WAV to MP3 lose quality?

Yes, MP3 is lossy by design. At 320 kbps the loss is hard to hear, and the file is 6.9 times smaller (2.4 versus 16.5 MB per minute). Keep the WAV if you will edit or re-encode.

What is the best MP3 bitrate for a DJ mix?

320 kbps CBR, which is 2.4 MB per minute or about 288 MB for a 2-hour set, is the common upload standard. LAME -V0 (about 245 kbps average) is a smaller alternative for personal listening.

Sources

Hannes Hennerbichler builds AirCheck and records his own DJ sets with it through a Focusrite Scarlett 8i6. Every step on this page was run on the macOS version stated above. Drafted with AI assistance, checked and edited by the author. About