Free converter · Remux (container swap)
Convert AAC to M4A
Short answer
Drop your AAC file into the converter below and download the M4A file. It runs in your browser with FFmpeg, for files up to 100 MB; nothing is uploaded. The video and audio streams are copied into the M4A container without re-encoding, so quality and file size stay the same. If a stream cannot go into M4A (PCM audio cannot go into MP4, for example), the converter re-encodes to AAC audio in M4A, audio only instead.
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 the M4A container; codecs match. · Remux (container swap) · Browser-side via FFmpeg WASM - nothing uploaded.
Key takeaways
- The audio stream was copied without re-encoding, and the 245 KB file became 244 KB (-0.3%). The raw stream checksums differ because ADTS and MP4 frame the same AAC packets differently; the decoded audio is identical.
- The result holds: Audio: aac 48000 Hz 2 ch.
- In your browser the same conversion of a 3 second clip took 0.03 seconds on the single-thread engine; natively, the 10 second clip took 0.05 seconds.
- Next to it: AAC to FLAC (+567%), AAC to MP3 (-34.2%), AAC to OGG (-51.2%).
Measured: AAC to M4A
The converter's own ffmpeg arguments, run on a 10 second 1920 × 1080 excerpt of Big Buck Bunny (an animated film, not camera footage) saved in AAC. The browser column is the same arguments on the single-thread WebAssembly core with a 3 second excerpt, in a headless run; your device will differ. Results describe this clip and these encoders.
| Check | Result |
|---|---|
| Mode | Streams copied (no re-encoding) |
| Input | AAC, 245 KB |
| Output | M4A, 244 KB (-0.3%) |
| Output streams | Audio: aac 48000 Hz 2 ch |
| Time, native, 10 s clip | 0.05 s |
| Time, browser engine, 3 s clip | 0.03 s |
| Audio checksum | Differs as stored; decoded audio identical |
Because nothing is decoded, a copy takes a fraction of a second whatever the length of the video.
AAC vs M4A
| AAC | M4A | |
|---|---|---|
| Full name | Advanced Audio Coding (raw stream) | MPEG-4 audio |
| What is inside | AAC audio without a container | AAC (or Apple Lossless) audio in an MP4 container |
| Compression | Lossy | Lossy or lossless |
| Best for | Players that take a bare AAC stream; M4A is the more common wrapper | Apple devices and voice memos |
What you get
The same streams in an M4A file. When a stream cannot be copied, the converter writes AAC audio in M4A, audio only.
Planning a bigger file
These are estimates scaled up from the 10 second clip. Real files differ with content, resolution and bitrate, so treat them as an order of magnitude, not a promise.
| Length of the video or recording | Input size (like ours) | M4A size | Time in your browser |
|---|---|---|---|
| 1 minute | 1.47 MB | 1.46 MB | 1 seconds |
| 10 minutes | 14.66 MB | 14.62 MB | 5 seconds |
| 1 hour | 87.95 MB | 87.73 MB | 32 seconds |
An AAC file of this kind reaches the 100 MB limit of the converter after about 72 minutes; converting it would take roughly 39 seconds on the single-thread engine, and the M4A would be about 104.59 MB.
AAC and M4A next to their neighbors
The same clip through other conversions with the same source or the same target.
| Conversion | How | Size change | Time (native) |
|---|---|---|---|
| AAC to M4A | Copy | -0.3% | 0.05 s |
| AAC to FLAC | Re-encode | +567% | 0.11 s |
| AAC to MP3 | Re-encode | -34.2% | 0.24 s |
| AAC to OGG | Re-encode | -51.2% | 0.22 s |
| AAC to Opus | Re-encode | -52.3% | 0.10 s |
| AAC to WAV | Re-encode | +686% | 0.09 s |
| AIFF to M4A | Re-encode | -91.5% | 0.28 s |
Choosing M4A
M4A: MPEG-4 audio. Apple devices and voice memos. AAC: Advanced Audio Coding (raw stream). Players that take a bare AAC stream; M4A is the more common wrapper.
- Use this conversion when a program wants the other container; the picture and sound stay exactly as they were.
- If the destination states the format it accepts, use that and nothing else.
Questions people ask
Is this AAC to M4A 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 AAC to M4A reduce quality?
Not when the streams fit M4A: they are copied unchanged. Only if a stream has to be re-encoded is there a small, usually invisible loss.
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.
How do I convert AAC to M4A?
Choose the file in the converter above and download the M4A. It runs in your browser with no upload.
Will converting AAC to M4A reduce quality?
No. The audio is copied, and the decoded audio was identical in our test.
Why did the file size change by -0.3%?
A copy only changes the container, so the size stays about the same.
How long does it take?
A 3 second clip took 0.03 seconds in the browser engine in our test; time grows with the length of the file.
How long will an AAC file of 100 MB take?
At the speed we measured in the browser engine, about 39 seconds for a file like our clip. Your device and the content will change it.
Is my file uploaded?
No. The conversion runs in your browser.
Is there a size limit?
Files up to 100 MB. The first conversion downloads a converter engine of about 30 MB once per visit.
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 2026-10-09)
- MDN: Web audio codec guide (read 2026-10-09)
- Blender Foundation: Big Buck Bunny (CC BY 3.0), the clip used for the measurements (read 2026-10-09)
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.