Free converter · Remux (container swap)
Convert M4A to AAC
Short answer
Drop your M4A file into the converter below and download the AAC 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 AAC container without re-encoding, so quality and file size stay the same. If a stream cannot go into AAC (PCM audio cannot go into MP4, for example), the converter re-encodes to AAC audio at about 128 kbps 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 extracted from M4A. · Remux (container swap) · Browser-side via FFmpeg WASM - nothing uploaded.
Key takeaways
- The audio stream was copied without re-encoding, and the 244 KB file became 245 KB (+0.2%). The AAC packets are copied, but an M4A carries start-trim information that a bare AAC file does not, so decoding the two files gives slightly different samples at the start.
- 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 0.07 seconds.
- Next to it: M4A to FLAC (+566%), M4A to OGG (-51.2%), M4A to Opus (-52.2%).
Measured: M4A to AAC
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 M4A. 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 | M4A, 244 KB |
| Output | AAC, 245 KB (+0.2%) |
| Output streams | Audio: aac 48000 Hz 2 ch |
| Time, native, 10 s clip | 0.07 s |
| Time, browser engine, 3 s clip | 0.03 s |
| Audio checksum | Different |
Because nothing is decoded, a copy takes a fraction of a second whatever the length of the video.
M4A vs AAC
| M4A | AAC | |
|---|---|---|
| Full name | MPEG-4 audio | Advanced Audio Coding (raw stream) |
| What is inside | AAC (or Apple Lossless) audio in an MP4 container | AAC audio without a container |
| Compression | Lossy or lossless | Lossy |
| Best for | Apple devices and voice memos | Players that take a bare AAC stream; M4A is the more common wrapper |
What you get
The same streams in an AAC file. When a stream cannot be copied, the converter writes AAC audio at about 128 kbps.
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) | AAC size | Time in your browser |
|---|---|---|---|
| 1 minute | 1.45 MB | 1.45 MB | 1 seconds |
| 10 minutes | 14.51 MB | 14.54 MB | 5 seconds |
| 1 hour | 87.05 MB | 87.25 MB | 31 seconds |
An M4A file of this kind reaches the 100 MB limit of the converter after about 72 minutes; converting it would take roughly 38 seconds on the single-thread engine, and the AAC would be about 105.09 MB.
M4A and AAC next to their neighbors
The same clip through other conversions with the same source or the same target.
| Conversion | How | Size change | Time (native) |
|---|---|---|---|
| M4A to AAC | Copy | +0.2% | 0.07 s |
| M4A to FLAC | Re-encode | +566% | 0.10 s |
| M4A to OGG | Re-encode | -51.2% | 0.26 s |
| M4A to Opus | Re-encode | -52.2% | 0.10 s |
| M4A to WAV | Re-encode | +686% | 0.08 s |
| AIFF to AAC | Re-encode | -91.5% | 0.26 s |
| AVI to AAC | Re-encode | -97.9% | 0.30 s |
Choosing AAC
AAC: Advanced Audio Coding (raw stream). Players that take a bare AAC stream; M4A is the more common wrapper. M4A: MPEG-4 audio. Apple devices and voice memos.
- 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 M4A to AAC 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 AAC reduce quality?
Not when the streams fit AAC: 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 M4A to AAC?
Choose the file in the converter above and download the AAC. It runs in your browser with no upload.
Will converting M4A to AAC reduce quality?
No re-encoding happens: the audio packets are copied. The AAC packets are copied, but an M4A carries start-trim information that a bare AAC file does not, so decoding the two files gives slightly different samples at the start.
Why did the file size change by +0.2%?
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 M4A file of 100 MB take?
At the speed we measured in the browser engine, about 38 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.