OneTaskBy Tim King · Updated
M4A to MP3 Converter
Private AAC Voice Memo and iTunes Audio Conversion, Decoded by Your Browser
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How the M4A To MP3 works
Drop in an M4A from an iPhone voice memo, iTunes or a phone recorder and download it as an MP3. This M4A to MP3 converter decodes the AAC audio with your browser's own decoder and re-encodes it at 128, 192 or 320 kbps. Nothing is uploaded, so private recordings stay on your device.
M4A to MP3: one lossy codec to another
M4A is an MPEG-4 container, almost always holding AAC audio. AAC is a newer, more efficient lossy codec than MP3: at the same bit rate it usually sounds better, which is why Apple uses it. The reason to convert is compatibility. Car stereos, older MP3 players, some podcast hosts and plenty of web forms accept MP3 but not M4A. Because both codecs are lossy, M4A to MP3 is a transcode: the AAC is decoded to plain samples and the MP3 encoder then discards detail again by its own rules.
What is lost in the transcode
- A second generation of loss. Artefacts from both encoders stack. Keep the original M4A as your master and treat the MP3 as a delivery copy.
- Bit rate. Pick a rate at or above the source. A 256 kbps iTunes AAC deserves 320 kbps MP3; a 64 kbps voice memo gains nothing from more than 128 kbps.
- Metadata. iTunes tags, chapter marks and artwork are not carried into the MP3.
- ALAC. Some M4A files hold Apple Lossless rather than AAC. Converting those to MP3 is lossless to lossy, a single generation of loss.
Browser support for M4A decoding
AAC in M4A decodes in Chrome, Edge, Safari on macOS and iOS, and Firefox on Windows and macOS, which use the operating system's decoder. Firefox on Linux needs the system FFmpeg libraries. Apple Lossless (ALAC) inside M4A decodes reliably only in Safari; Chrome and Firefox usually refuse it, and the page will say the file could not be decoded.
How to read the stats
Source shows channels, decoded sample rate, length and original size. Output is the MP3 bit rate selected and Output size estimates the MP3 file, which is bit rate × seconds. MP3 export supports the standard MPEG rates, so a 44.1 or 48 kHz source encodes directly.
Need an editable copy instead? Use M4A to WAV. Raw AAC files use the AAC to MP3 page, and lossless sources go through FLAC to MP3.
FAQ
Will converting M4A to MP3 reduce quality?
Slightly, yes. Both formats are lossy, so the MP3 encoder discards detail on top of what the AAC encoder already removed. At 320 kbps the difference is very hard to hear; at 128 kbps it can be noticeable on music with cymbals or applause.
Which bit rate should I choose for M4A to MP3?
Match or exceed the source. iTunes purchases are 256 kbps AAC, so choose 320 kbps. Voice memos and phone recordings are usually 64 to 128 kbps, and 128 kbps MP3 is plenty for them. The size line shows the result for each choice.
Why does my M4A file fail to open?
It may hold Apple Lossless audio, which only Safari decodes, or it may be DRM-protected, which no browser tool can read. Old iTunes purchases with FairPlay protection end in .m4p rather than .m4a. Try Safari for ALAC files.
Is my M4A uploaded anywhere?
No. The file is decoded, processed and encoded inside your browser with the Web Audio API. Nothing is sent to a server, so it works offline once the page has loaded and your audio stays private.
See also: all Audio & Video tools, Units, Images, Documents, Data & Code.
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