Audio
M4A vs MP3: Which Is Better, and When It Matters
M4A is usually better than MP3: it holds AAC audio, which tends to sound as good as MP3 at a lower bitrate. MP3 is better only when you need a file that plays on any device ever made. For music on Apple devices, keep M4A. For sharing with unknown players, use MP3.
What is the difference between M4A and MP3?
They are not the same kind of thing. MP3 is both a codec and a file format. M4A is a container, an MPEG-4 audio file, and it normally holds audio encoded with AAC. So “AAC vs MP3” is the real codec comparison, and “M4A vs MP3” is what people search.
AAC was designed as MP3’s successor. Both are lossy: they throw away detail you are unlikely to hear to make the file small. Neither can be turned back into the original recording.
Is M4A smaller than MP3 at the same quality?
In our test, at a 128 kbps target, yes. We encoded two clips with Apple’s
afconvert| Clip | WAV source | M4A (AAC) | MP3 |
|---|---|---|---|
| 20 s tone and noise mix | 3,528,078 bytes | 278,668 bytes (111 kbps) | 321,036 bytes (128 kbps) |
| 5.6 s synthetic speech | 974,750 bytes | 64,849 bytes (93 kbps) | 89,487 bytes (130 kbps) |
Two cautions. The AAC encoder landed below its 128 kbps target, so part of the saving is that it simply used fewer bits. And we did not run a listening test, so we make no claim that the two sound identical at those sizes. Judge by ear for music you care about. Our audio bitrate guide shows how to choose a bitrate.
Does M4A play everywhere MP3 does?
No. MP3 plays on essentially everything, including old car stereos, cheap MP3 players, and any upload form that lists audio. M4A plays on every Mac, iPhone, iPad, and modern Windows and Android device, but older hardware and some web tools reject it.
M4A also covers more than AAC. Apple Lossless audio uses the same extension, so two M4A files can be very different sizes. Check with
afinfo song.m4aShould I use M4A or MP3?
| Situation | Use |
|---|---|
| Music for iPhone, Mac or Apple Music | M4A |
| Voice Memos you keep on Apple devices | M4A (it is what Voice Memos records) |
| Podcast feed or file sent to unknown listeners | MP3 |
| Old car stereo, USB stick, DJ gear | MP3 |
| Upload form that only lists MP3 | MP3 |
| Master you may edit again | WAV or FLAC, not either lossy format |
Do not convert M4A to MP3 and back for fun. Each lossy conversion discards a little more. If you must convert, do it once, from the best source you have.
What bitrate should I pick?
Bitrate matters more than the format. Use a higher number for music and a lower one for speech. The values below are rules of thumb we use, not measurements, so check by listening on the speakers or headphones you actually use.
| Content | Starting point | Why |
|---|---|---|
| Music you care about | 192 to 256 kbps | Room for cymbals and reverb tails |
| Casual music, small phone | 128 kbps | The size we tested above |
| Spoken word, podcasts | 64 to 96 kbps | Voices need far fewer bits |
| Voice notes | 32 to 64 kbps | Intelligible, tiny files |
A higher bitrate cannot repair a file that is already lossy. If your source is a 128 kbps MP3, saving it as 320 kbps M4A only makes it bigger.
How do I convert M4A to MP3 on a Mac?
Music can do it: open Music > Settings > Files > Import Settings, choose the MP3 Encoder, then select the song in your library and use File > Convert > Create MP3 Version. It makes a second copy and leaves the original.
afconvertafconvert song.wav song.m4a -f m4af -d aac -b 128000For the full walkthrough see convert M4A to MP3 on Mac. For a folder, see batch convert audio on Mac.
When is Smol the wrong tool for this?
If you need one file in AAC,
afconvertSmol earns its $29 (once, one Mac) when you have a whole folder of mixed audio. It compresses audio to M4A, AAC or MP3 with a bitrate from 16 to 512 kbps, converts between M4A, MP3, WAV, FLAC and OGG, runs from a Finder right-click, and uploads nothing. See pricing or the best audio converter for Mac.
How we checked this
Encoded a 20 s synthetic tone mix and a 5.6 s macOS speech clip from WAV to AAC M4A with afconvert and to MP3 with ffmpeg at a 128 kbps target, then read sizes and average bitrates with ffprobe. Facts last checked . We make Smol, so treat our claims about it with the same care as any vendor’s, and see our editorial policy.
M4A vs MP3: common questions
Is M4A better quality than MP3?
At the same bitrate AAC, the codec inside most M4A files, is generally rated equal or better than MP3. In our test AAC also produced a smaller file at a 128 kbps target. Quality still depends on the encoder and the bitrate, so listen before you batch convert.
Is M4A lossless?
Usually not. Most M4A files hold lossy AAC. The extension can also hold Apple Lossless (ALAC), which is lossless and much larger. Run afinfo on the file in Terminal to see which codec it contains.
Is AAC better than MP3?
Mostly yes. AAC was built as the successor and typically needs fewer bits for similar sound. MP3 wins on compatibility, since almost every device and website accepts it. Pick on where the file will be played, not on a small quality difference.
Can I play M4A on Windows or Android?
Yes on current versions of both, since AAC is a mainstream codec. Older players, some car stereos and some upload forms still refuse M4A. If you are unsure who will open it, send an MP3.
Does converting M4A to MP3 reduce quality?
Yes. Both are lossy, so decoding and re-encoding discards more detail. At a high bitrate the loss is hard to hear once, but it adds up if you convert repeatedly. Convert once from the original when you can.
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