Convert M4A to MP3
The format your iPhone records in, in the one everything reads.
Drop files here
or click to choose from your deviceAccepted: M4A, MP4
Up to 3 files per runUp to 150 MB per file5 runs per dayRemove limits with Pro✓ Works offline
Your files stay on your device
This tool runs entirely in your browser. Nothing is uploaded, nothing is stored, and you can even turn off your internet connection before you start.
Example
Example: a 35-minute sermon from an iPhone voice memo as an MP3 for a church podcast
A church records the Sunday sermon with Voice Memos on an iPhone and posts it on its website, whose podcast host takes MP3 only. The file is sermon.m4a: 35 minutes, 16.4 MB, well under the free 150 MB a file. Settings: Bit rate 96 kbps, Channels Mix down to mono.
- The memo is decoded by the browser, the same way it would play it, and mixed to one channel: a single voice loses nothing in mono.
- LAME writes it at a constant 96 kbps: 96,000 bits, or 12,000 bytes, every second, whatever is being said.
- 35 minutes is 2,100 seconds, so the MP3 is 2,100 × 12,000 bytes = 25.2 MB. It is larger than the M4A because AAC is the more efficient codec.
- Download sermon.mp3 and upload it to the podcast host. Any title in the M4A’s tags comes along in the MP3; the episode title and artwork listeners see are set on the host’s form.
| Bit rate | 35 minutes as MP3 | The page calls it |
|---|---|---|
| 64 kbps | 16.8 MB | speech |
| 96 kbps | 25.2 MB | |
| 128 kbps | 33.6 MB | |
| 192 kbps | 50.4 MB | a good default |
| 320 kbps | 84.0 MB | highest |
sermon.mp3, 35 minutes and 25.2 MB, which every podcast app and older car stereo plays. At a constant bit rate the size is simply bit rate × length ÷ 8, so a one-hour service at 96 kbps would be 43.2 MB.
How it works
- Drop the .m4a files on the box.
- For a voice memo, 96 or 128 kbps mono is plenty and keeps the file small.
- For music, use 256 or 320 to keep the second encode from showing.
- Download the MP3s.
Frequently asked questions
- Where do .m4a files come from?
- Voice Memos on an iPhone, most Apple recording apps, and anything that saves AAC in an MP4 container. It is a perfectly good format; the trouble is that older car stereos, some upload forms and a lot of older software only know MP3.
- Is MP3 worse than M4A?
- At the same bit rate, yes, slightly — AAC is the newer codec and more efficient, particularly below 128 kbps. Converting is therefore a small step down, which is why it is worth choosing a higher bit rate than the original rather than matching it.
- Will a protected file work?
- No. Old purchases from the iTunes Store with DRM (.m4p) cannot be decoded and will be refused. Ordinary .m4a files, including everything Voice Memos produces, convert fine.
- Are the title, artist and cover art kept?
- Yes. The title, artist, album, album artist, track number, year, genre and front cover in the file’s tags are written into the MP3 as an ID3v2.3 tag, the kind car stereos and phones read. A file without tags gives an MP3 without tags; add them in your player or in something like Mp3tag.
- Does mono make the MP3 smaller?
- No. The MP3 is written at a constant bit rate, so its size depends only on the bit rate and the length: 96 kbps is 12,000 bytes a second in mono or in stereo. What mono changes is the sound: for one voice on one microphone nothing is lost, and the encoder has a single channel to spend its bits on.
- How big will the MP3 be?
- Bit rate × seconds ÷ 8. A minute is 480 KB at 64 kbps, 720 KB at 96, 960 KB at 128, 1.44 MB at 192 and 2.4 MB at 320. The free 150 MB limit applies to the M4A you add, not to the MP3 you get.
- What are the free limits?
- Three files per run, 150 MB per file and 5 runs a day. Pro removes all three.