Compress M4A files
Shrink iPhone voice memos, lectures and music files in M4A, right in your browser.
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How to compress M4A files
Add your files
Drop files on the box, paste them or choose them from your device. Nothing is uploaded.
Check the settings
The default preset suits most files. Change quality, size or format if you need a smaller file.
Download the result
Save each file or all of them as one ZIP. If a file cannot get smaller, you keep the original.
What an M4A file is
M4A is simply an MP4 file that contains only audio. Apple introduced the extension with iTunes in the early 2000s so that music players could tell audio files apart from videos. The file uses the same box structure as an MP4 video, which gives it an index for instant seeking, proper duration display, tags, chapters and cover art.
Two very different codecs can live inside an M4A:
- AAC (lossy), by far the most common: iPhone Voice Memos, purchases from the iTunes Store, many Android recorder apps and audio extracted from videos.
- ALAC (Apple Lossless), used for lossless CD rips in Apple Music and iTunes. ALAC files are several times larger than AAC ones and roughly the size of FLAC.
You cannot tell which one you have from the extension. A quick hint is the size: under 2 MB per minute is AAC; 5 MB per minute or more is almost certainly ALAC. The difference matters here: browsers have no ALAC decoder, so the tool can compress AAC files but shows a message for ALAC ones.
Voice memos and recordings
The most common reason to compress an M4A is a long recording: a lecture, a meeting, an interview or a rehearsal made with the iPhone's Voice Memos app or a similar recorder. Depending on the "Audio Quality" setting (Compressed or Lossless), Voice Memos writes AAC or ALAC, and the lossless option fills storage quickly. Memos recorded as Compressed (AAC) can go straight into the tool; for lossless ones, switch the setting to Compressed for future recordings and convert existing files to AAC or WAV on a computer first, for example in Apple's Music app or VLC.
Speech does not need stereo or a high bitrate. Converting a two-hour lecture recording to mono MP3 at 64 kbps turns it into a file of about 58 MB that you can send through most messengers, and the voice stays perfectly clear. At 48 kbps it is still very intelligible and about 43 MB. Choose MP3 or Opus as the output for this: the AAC encoder in Chrome and Edge on Windows goes no lower than 96 kbps, which gives about 86 MB.
Settings for M4A files
| Source | Output | Why |
|---|---|---|
| Voice memo, lecture, meeting | MP3 or Opus, mono, 48–64 kbps | Speech stays clear at a fraction of the size |
| Music in AAC 256 kbps | AAC, stereo, 128–160 kbps | Saves space on a phone; keep the original if you have room |
| ALAC music, converted to WAV first | AAC, stereo, 192 kbps | Large reduction with sound most people cannot tell apart from the lossless file |
| ALAC music you want to keep lossless, converted to WAV first | FLAC, Bit depth Keep original | Same audio, comparable size, more widely supported outside Apple's ecosystem |
AAC output is written as an M4A again (in Firefox, which cannot create AAC, as Opus instead), so it opens in Apple Music, QuickTime, Windows Media Player and the Photos and Files apps on phones. If the recording starts or ends with long silence, "Trim silence at start and end" is the most painless saving of all.
Common problems
- "File is not supported" on an upload form. Some forms accept only MP3. Choose MP3 as the output format, or ask whether M4A or AAC is allowed.
- Protected files. Old iTunes purchases from before 2009 can be M4P files with copy protection. They cannot be decoded by any browser.
- Chapters disappear. Audiobooks in M4A or M4B often have chapter marks. The compressed file does not keep them, so keep the original audiobook.
M4A questions
Is M4A better than MP3?
When it contains AAC, it usually sounds better at the same bitrate and seeks reliably. MP3 is still the safer choice for very old players and some car stereos.
What is the difference between M4A and M4B?
Both are MP4 audio files. M4B is used for audiobooks so that players remember the playback position and show chapters.
Why is my M4A so big?
It is probably ALAC, Apple's lossless codec, or an AAC file at a high bitrate. Converting ALAC to AAC brings the biggest saving; do that in the Music app or VLC, because browsers cannot decode ALAC.
Can I open M4A on Windows or Android?
Yes. Windows 10 and 11 play AAC in M4A natively, and Android has supported it since its first versions. ALAC playback depends on the app.
More audio tools
For raw AAC streams see AAC; for all formats, the audio compressor. To see how files are processed on your device, read how it works.