Free converter · Extract audio
Convert MP4 to AAC
Short answer
Drop your MP4 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. Only the sound is kept: the video track is dropped and the audio is saved as AAC audio at about 128 kbps.
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.
Extract audio from MP4 into AAC. · Extract audio · Browser-side via FFmpeg WASM - nothing uploaded.
Key takeaways
- The 8.88 MB MP4 file became a 164 KB AAC file (-98.2%), about 127 kbps for the 10 second clip.
- The result holds: Audio: aac 48000 Hz 2 ch.
- In your browser the same conversion of a 3 second clip took 0.25 seconds on the single-thread engine; natively, the 10 second clip took 0.30 seconds.
- Next to it: MP4 to AVI (-70.6%), MP4 to FLAC (-81.7%), MP4 to GIF (+592%).
Measured: MP4 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 MP4. 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 | Audio re-encoded |
| Input | MP4, 8.88 MB |
| Output | AAC, 164 KB (-98.2%) |
| Output streams | Audio: aac 48000 Hz 2 ch |
| Time, native, 10 s clip | 0.30 s |
| Time, browser engine, 3 s clip | 0.25 s |
A re-encode decodes and encodes every frame or sample, so the time grows with the length of the file.
MP4 vs AAC
| MP4 | AAC | |
|---|---|---|
| Full name | MPEG-4 Part 14 | Advanced Audio Coding (raw stream) |
| What is inside | H.264 or H.265 video with AAC audio | AAC audio without a container |
| Compression | Depends on the codec inside | Lossy |
| Best for | Uploading anywhere: the format social platforms document first | Players that take a bare AAC stream; M4A is the more common wrapper |
What you get
AAC audio at about 128 kbps. Extract audio from MP4 into AAC.
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 | 51.38 MB | 949 KB | 5 seconds |
| 10 minutes | 513.80 MB | 9.49 MB | 50 seconds |
| 1 hour | 3082.80 MB | 56.96 MB | 5.0 minutes |
An MP4 file of this kind reaches the 100 MB limit of the converter after about 2.0 minutes; converting it would take roughly 10 seconds on the single-thread engine, and the AAC would be about 1.94 MB.
MP4 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) |
|---|---|---|---|
| MP4 to AAC | Re-encode | -98.2% | 0.30 s |
| MP4 to AVI | Re-encode | -70.6% | 1.6 s |
| MP4 to FLAC | Re-encode | -81.7% | 0.13 s |
| MP4 to GIF | Re-encode | +592% | 5.5 s |
| MP4 to M4A | Re-encode | -98.2% | 0.29 s |
| MP4 to MKV | Copy | -0.1% | 0.13 s |
| MP4 to OGG | Re-encode | -98.7% | 0.25 s |
Choosing AAC
AAC: Advanced Audio Coding (raw stream). Players that take a bare AAC stream; M4A is the more common wrapper. MP4: MPEG-4 Part 14. Uploading anywhere: the format social platforms document first.
- Keep your original: a re-encode is a copy of a copy.
- If the destination states the format it accepts, use that and nothing else.
Questions people ask
Is this MP4 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 MP4 to AAC reduce quality?
The audio is re-encoded to AAC, a lossy format, so there is a small loss compared with the original track.
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 MP4 to AAC?
Choose the file in the converter above and download the AAC. It runs in your browser with no upload.
Will converting MP4 to AAC reduce quality?
A little, because AAC is lossy. Keep the original file.
Why did the file size change by -98.2%?
The target codec and settings decide the size. This 10 second clip came out at 164 KB, about 127 kbps.
How long does it take?
A 3 second clip took 0.25 seconds in the browser engine in our test; time grows with the length of the file.
How long will an MP4 file of 100 MB take?
At the speed we measured in the browser engine, about 10 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.