Manatee

How to convert MP4 to MP3 (extract the audio) on a Mac

· 6 min read

The direct route on a Mac is Manatee: drop the MP4 into Convert, choose MP3, and you get an audio file with the video discarded. Built-in tools can do it too, but in two steps: QuickTime Player exports an audio-only M4A, and the Music app converts that M4A to MP3. If the destination accepts M4A, stop after QuickTime; that copy is lossless, while an MP3 is always re-encoded.

MP3 or M4A: decide before you convert

Almost every MP4 carries its audio as AAC. An M4A file is just that AAC stream in an audio-only container. Extracting to M4A means copying the audio out untouched, with no change in quality and no encoding time.

MP3 is a different codec, so producing one means decoding the AAC and re-encoding it. Done at a decent bitrate (192 kbps or higher), the loss is hard to hear, but it is a second lossy generation, and the file is often larger than the M4A for the same quality. MP3’s advantage is that it plays on everything ever made: old car stereos, cheap voice recorders, web players, presentation software, and anything that says “MP3 only.”

So: if the file is for your own phone or Mac, a podcast app, or a modern website, choose M4A. If it is for a device or service that specifically wants MP3, choose MP3. Lossless vs lossy has the longer version of this trade-off.

Convert with Manatee

Manatee accepts MP4 (and MOV, MKV, WebM, AVI, and the rest of its video inputs) and offers MP3, M4A, WAV, and FLAC as audio targets. It runs on macOS 12 Monterey or later, on Apple silicon and Intel, and the conversion happens on your Mac with nothing uploaded.

  1. Open Manatee and choose Convert.
  2. Drop the MP4 into the window. Dropping a folder of videos queues all of them.
  3. Choose MP3 as the target. Choose M4A instead if you want the original audio untouched.
  4. Click Convert. The audio file is written next to the video; the MP4 is never modified.

Manatee extracts the whole soundtrack. It does not trim a section, fade, normalize volume, split chapters, or pick one of several audio tracks from a file with multiple languages (it takes the default track). Those are editing tasks. If you want a ringtone, a clip, or a cleaned-up recording, extract the full audio first, then trim it in QuickTime Player (Edit > Trim) or an audio editor.

Two-step method with QuickTime Player and Music

This works on any Mac without installing anything, and it produces an MP3 if you follow both steps.

Step one: export audio only from QuickTime Player.

  1. Open the MP4 in QuickTime Player.
  2. Choose File > Export As > Audio Only.
  3. Name the file and click Save. You get an .m4a containing the original AAC audio.

If QuickTime cannot open the MP4 at all, the file’s codecs are not ones macOS supports; see why an MP4 can still refuse to play. Manatee reads such files because it bundles its own decoders.

Step two: convert the M4A to MP3 in Music.

  1. Open the Music app and choose Music > Settings > Files (on older versions, Preferences > Files).
  2. Click Import Settings, set Import Using to MP3 Encoder, pick a quality (Higher Quality, 192 kbps, is a good default), and click OK.
  3. Drag the .m4a into the Music window so it is added to your library.
  4. Select it and choose File > Convert > Create MP3 Version.
  5. The MP3 appears in the library beside the M4A. Right-click it and choose Show in Finder to find the file, then copy it wherever you need.

Afterward, you may want to delete both tracks from Music so they do not clutter your library, and set Import Settings back to AAC if you rip CDs.

From Terminal with ffmpeg

If ffmpeg is installed on your Mac (it is not included with macOS), one command does either job.

Lossless M4A:

ffmpeg -i video.mp4 -vn -c:a copy audio.m4a

MP3 at good quality:

ffmpeg -i video.mp4 -vn -c:a libmp3lame -q:a 2 audio.mp3

-vn drops the video stream. -q:a 2 asks for a variable bitrate averaging around 190 kbps; use -b:a 320k for a fixed 320 kbps instead. If the MP4 has several audio tracks, add -map 0:a:1 to select the second one.

Quality and size: what to expect

An hour of stereo AAC at 128 kbps inside an MP4 is roughly 55 MB of audio. Extracted to M4A it stays about 55 MB. Re-encoded to 192 kbps MP3 it becomes about 85 MB, and it does not sound any better than the M4A; MP3 simply needs more bits to reach the same quality.

Re-encoding cannot add quality. If the MP4’s audio was a low-bitrate mono recording from a webcam, the MP3 will be the same recording. Choosing 320 kbps only makes the file larger.

A speech recording can go down to 96 or 128 kbps MP3 without audible loss. Music should stay at 192 kbps or above.

Metadata does not carry over automatically. An MP4’s title and artwork live in video-style tags, and most extraction tools write a bare audio file. Add a title and artwork in the Music app (select the track, choose Song > Info) if you want them on the MP3.

Questions

Can I extract audio from a MOV or MKV the same way?

Yes. QuickTime’s Audio Only export works on any file it can play, including MOV. MKV, WebM, and AVI are not supported by QuickTime; Manatee and ffmpeg handle them directly.

Why is my exported audio silent?

The MP4 contained an audio codec that the exporting tool could not decode, or the file had multiple audio tracks and the first was empty. Try a different tool, or pick a different track with the ffmpeg -map option.

Can I get the audio as WAV for editing?

Yes. Manatee and ffmpeg both output WAV, which is uncompressed and ideal for editing, at roughly 10 MB per minute of stereo.

Does converting to MP3 shrink the file enough to email?

Usually. Dropping the video is what makes the difference. A ten-minute 1080p video of 500 MB becomes a 15 MB MP3. For getting the video itself under a limit, see how to compress a video to email it from a Mac.