Convert MP4 to MP3 on Mac

Install ffmpeg once with Homebrew, then run the command in the folder that holds the video:

brew install ffmpeg
ffmpeg -i in.mp4 -vn -c:a libmp3lame -b:a 192k out.mp3

-vn drops the video, -c:a libmp3lame picks the MP3 encoder, and -b:a 192k sets the bitrate. 128k is fine for speech. 192k to 256k suits music. The output is a new file, so your MP4 is untouched.

Want a whole folder? Loop it:

for f in *.mp4; do ffmpeg -n -i "$f" -vn -c:a libmp3lame -b:a 192k "${f%.mp4}.mp3"; done

No. QuickTime Player exports audio only as M4A (AAC). Open the video, choose File > Export As > Audio Only, name the file and save. You get an .m4a, which plays on every Apple device and in most apps.

If a site or device insists on .mp3, M4A will not do and you need the ffmpeg route above. Renaming .m4a to .mp3 does not convert anything and the file will often fail to open. See the M4A to MP3 guide if you already have an M4A.

It reads video files and writes audio, but not MP3. On macOS 27.0.1 we tried afconvert -f MPG3 -d .mp3 on an MP4 and it failed with a format error. It does write M4A and WAV straight from the video:

afconvert -f mp4f -d aac -b 192000 in.mp4 out.m4a
afconvert -f WAVE -d LEI16 in.mp4 out.wav

Set the bitrate yourself. With no -b flag, our 20 second clip came out at about 51 kbps, far below the source audio.

We extracted the audio of one 20 second MP4 on an Apple Silicon Mac. The source audio was AAC at about 152 kbps, mono, 48 kHz. It came from a generated sine tone, so the quality is not meaningful, but the sizes follow the bitrate.

Size is bitrate times length, so a one hour MP3 at 192 kbps is about 86 MB. See audio bitrate explained for what the numbers mean.

Yes, a little, and it cannot be undone. The audio inside most MP4 files is already AAC. Turning AAC into MP3 decodes it and encodes it again, which is two rounds of lossy compression. At 192 kbps or above the difference is hard to hear. Below 128 kbps music starts to sound thin.

If you do not need MP3 specifically, copying the original audio stream into an M4A loses nothing: ffmpeg -i in.mp4 -vn -c:a copy out.m4a. That works when the MP4 holds AAC audio, which is the usual case for phone and screen recordings. Our extract audio from video guide covers it.

For this exact job, Smol is the wrong tool. We tested it: Smol converts video to MP4, MOV, WebM or MKV, and audio to M4A, MP3, WAV, FLAC or OGG, but it will not take an MP4 and write an MP3. Use ffmpeg or QuickTime, as above.

Where Smol helps is after the extraction. Once you have audio files, it can shrink or convert a whole mixed folder at once, from your Finder, with nothing uploaded. That is $29 once, on the buy page. Compare options in the best audio converter for Mac.