Free converter · Extract audio
Convert MKV to AAC
Short answer
Drop your MKV 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 MKV into AAC. · Extract audio · Browser-side via FFmpeg WASM - nothing uploaded.
Key takeaways
- The 8.88 MB MKV file became a 167 KB AAC file (-98.1%), about 141 kbps for the 9 second clip.
- The result holds: Audio: aac 48000 Hz 2 ch.
- In your browser the same conversion of a 3 second clip took 0.16 seconds on the single-thread engine; natively, the 10 second clip took 0.25 seconds.
- Next to it: MKV to AVI (-70.6%), MKV to FLAC (-81.6%), MKV to GIF (+592%).
Measured: MKV 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 MKV. 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 | MKV, 8.88 MB |
| Output | AAC, 167 KB (-98.1%) |
| Output streams | Audio: aac 48000 Hz 2 ch |
| Time, native, 10 s clip | 0.25 s |
| Time, browser engine, 3 s clip | 0.16 s |
A re-encode decodes and encodes every frame or sample, so the time grows with the length of the file.
MKV vs AAC
| MKV | AAC | |
|---|---|---|
| Full name | Matroska | Advanced Audio Coding (raw stream) |
| What is inside | Almost any codec, plus several audio and subtitle tracks | AAC audio without a container |
| Compression | Depends on the codec inside | Lossy |
| Best for | Archiving and playback in desktop players; most social platforms do not list it | 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 MKV into AAC.
Planning a bigger file
These are estimates scaled up from the 9 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 | 56.24 MB | 1.06 MB | 3 seconds |
| 10 minutes | 562.42 MB | 10.55 MB | 32 seconds |
| 1 hour | 3374.52 MB | 63.33 MB | 3.2 minutes |
An MKV file of this kind reaches the 100 MB limit of the converter after about 1.9 minutes; converting it would take roughly 6 seconds on the single-thread engine, and the AAC would be about 1.97 MB.
MKV 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) |
|---|---|---|---|
| MKV to AAC | Re-encode | -98.1% | 0.25 s |
| MKV to AVI | Re-encode | -70.6% | 1.5 s |
| MKV to FLAC | Re-encode | -81.6% | 0.12 s |
| MKV to GIF | Re-encode | +592% | 5.3 s |
| MKV to M4A | Re-encode | -98.1% | 0.27 s |
| MKV to MOV | Copy | +0.1% | 0.10 s |
| MKV 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. MKV: Matroska. Archiving and playback in desktop players; most social platforms do not list it.
- 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 MKV 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 MKV 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 MKV to AAC?
Choose the file in the converter above and download the AAC. It runs in your browser with no upload.
Will converting MKV to AAC reduce quality?
A little, because AAC is lossy. Keep the original file.
Why did the file size change by -98.1%?
The target codec and settings decide the size. This 9 second clip came out at 167 KB, about 141 kbps.
How long does it take?
A 3 second clip took 0.16 seconds in the browser engine in our test; time grows with the length of the file.
How long will an MKV file of 100 MB take?
At the speed we measured in the browser engine, about 6 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.