Free converter · Lossy re-encode
Convert M4A to MP3
Short answer
Drop your M4A file into the converter below and download the MP3 file. It runs in your browser with FFmpeg, for files up to 100 MB; nothing is uploaded. The file is re-encoded to MP3 audio at about 128 kbps, keeping the source's sample rate. Re-encoding takes longer than a container swap and costs some quality; how much depends on the clip and on the quality setting, and at the converter's default setting the loss can be visible, so keep the original.
Maximum file size: 100 MB. The first conversion loads a ~30 MB converter engine, once per visit. Nothing is uploaded - conversion runs on your device.
AAC inside M4A re-encoded to MP3. · Lossy re-encode · Browser-side via FFmpeg WASM - nothing uploaded.
Key takeaways
- M4A usually holds AAC; MP3 is a different lossy codec, so this is a second lossy encode.
- Measured: a 192 kbps AAC M4A (242,765 bytes) became a 128 kbps MP3 (160,848 bytes), 33.7% smaller and lower in bitrate.
- The converter's default of 128 kbps can be below your source's bitrate; set -b:a or -q:a yourself in a terminal for better results.
- Keep the M4A if the destination plays it: it is the better-quality file.
Measured: what the conversion does to the file
Measured on the soundtrack of a 10 second excerpt of Big Buck Bunny (animated film; (c) Blender Foundation, CC BY 3.0), stereo, 48 kHz, using the same ffmpeg arguments this converter passes to its WebAssembly build, run with ffmpeg 6.1.1. Results describe this file.
| Check | Result |
|---|---|
| Input | M4A, AAC 192 kbps stereo, 242,765 bytes |
| Output | MP3, 128 kbps, 160,848 bytes (-33.7%) |
| Sample rate and channels | 48 kHz stereo, unchanged |
| Time, native ffmpeg | 0.25 s |
Smaller is not better here: a lower bitrate means less audio information, and AAC to MP3 compounds two lossy encodes.
M4A vs MP3
| M4A | MP3 | |
|---|---|---|
| Full name | MPEG-4 audio | MPEG-1 Audio Layer III |
| What is inside | AAC (or Apple Lossless) audio in an MP4 container | MP3 audio |
| Compression | Lossy or lossless | Lossy |
| Best for | Apple devices and voice memos | Music and podcasts that must play on every device |
What you get
MP3 audio at about 128 kbps, keeping the source's sample rate. AAC inside M4A re-encoded to MP3.
Closer to the source's quality
ffmpeg -i in.m4a -codec:a libmp3lame -b:a 192k out.mp3matches the source's bitrate.ffmpeg -i in.m4a -codec:a libmp3lame -qscale:a 2 out.mp3uses variable bitrate; the FFmpeg wiki says 0 to 3 normally produce transparent results.- The wiki calls 320 kbps generally wasteful for MP3.
When you need MP3 at all
MP3 plays on almost every device and in older software. If your player handles M4A or AAC, keep the original. If a service requires MP3, convert once from the best source you have and do not convert an MP3 again.
Questions people ask
Is this M4A to MP3 converter free and private?
Yes. It is free, needs no account and runs entirely in your browser, so the file never leaves your device.
Will converting M4A to MP3 reduce quality?
Some, because MP3 is lossy and the file is re-encoded. How much depends on the clip and on the quality setting, and at the converter's default setting the loss can be visible, so keep the original. For uploads, the platform re-encodes again anyway.
Is there a file size limit?
Files up to 100 MB. The first conversion downloads a converter engine of about 30 MB once per visit; larger files are better handled by a desktop app such as HandBrake or FFmpeg.
Does M4A to MP3 reduce quality?
Yes. It is lossy to lossy; with this converter the bitrate also drops from 192 to 128 kbps in our test.
Why is the MP3 smaller?
The converter's default is 128 kbps. Our M4A was 192 kbps.
How do I keep better quality?
Use a terminal with -b:a 192k or -q:a 2, or keep the M4A.
Is M4A the same as AAC?
M4A is an MP4 container that usually holds AAC audio.
More converters
Sources and how we checked
- MDN: Media container formats
- MDN: Web audio codec guide
- MDN: Image file type and format guide
- FFmpeg documentation: stream copy
- FFmpeg Documentation: ffmpeg (stream selection, -map, -c copy) (read 2026-10-08)
- FFmpeg Wiki: Encode/MP3 (libmp3lame quality and bitrate) (read 2026-10-08)
- FFmpeg Wiki: Encode/AAC (bitrate rule of thumb) (read 2026-10-08)
- Blender Foundation: Big Buck Bunny (CC BY 3.0), the clip used for the measurements (read 2026-10-08)
Reviewed October 8, 2026. What the converter writes was measured with ffprobe on the same FFmpeg build your browser downloads; format descriptions follow MDN's media guides.