How to convert MKV to MP4
Drop your MKV files into the box above, or click Choose files. You can add several at once.
Choose a quality. It only matters if the video has to be re-encoded; compatible videos are copied without any loss.
Click Convert to MP4. Files are processed on your device; a few minutes of media usually takes seconds.
Download the MP4 files one by one, or all at once as a ZIP.
Why convert MKV to MP4?
MKV is a flexible container that's great for recording, which is why OBS uses it by default: a crash doesn't corrupt the file. But video editors, phones, TVs and upload sites generally prefer MP4.
Most MKV recordings already contain H.264 video and AAC audio, so converting just moves the streams into an MP4 container. It's fast and lossless.
Game captures and screen recordings are large. Converting on your device avoids uploading gigabytes to a server.
MKV vs MP4
MKV can hold almost any codec, plus several audio and subtitle tracks. MP4 is less flexible but universally supported.
When the MKV contains H.264, the conversion copies it unchanged. Other codecs, such as VP9 or HEVC, are re-encoded to H.264. The first video and audio track are kept; subtitles and extra audio tracks are not.
| Property | MKV | MP4 |
|---|---|---|
| Typical video codec | Almost anything: H.264, HEVC, VP9, AV1 | H.264 (AVC), sometimes H.265 or AV1 |
| Typical audio codec | Almost anything, often several tracks | AAC |
| File size | Depends on the codecs inside | Efficient |
| Best for | Archiving films with multiple audio and subtitle tracks | Sharing and uploading video anywhere |
| Support | VLC and desktop players; not iPhones or most browsers | Every phone, browser, TV and editing app |
Is it safe?
Yes. MKV to MP4 runs entirely in your browser. Your files are read and converted by your own device using built-in browser technology, so they are never uploaded to a server and nobody else can see them.
You can check this yourself: open your browser's developer tools, switch to the Network tab and convert a file. No upload requests are made.
Videos are processed by your browser's own media engine (WebCodecs), usually with hardware acceleration. Nothing is uploaded, which also makes the conversion start instantly, however big the file.
Files stay in this tab's memory only until you remove them or close the page.
Frequently Asked Questions
Why does OBS record MKV?
If OBS or your computer crashes mid-recording, an MKV file stays playable up to that point, while an MP4 could be lost. Converting afterwards gives you the best of both.
Will my video be re-encoded?
Only if necessary. H.264 video, the OBS default, is copied without re-encoding. The result tells you which happened.
What happens to extra audio tracks and subtitles?
The main video and audio tracks are kept. Additional audio tracks (for example a separate microphone track) and subtitles are not included in the MP4.
Which browser works best?
Current Chrome, Edge and Safari support hardware video encoding and decoding. Firefox works for most files but can't decode HEVC. If a file can't be processed, you'll see a message saying why.
Is there a size limit?
Each video can be up to 1 GB. Files are read from disk in pieces, so they don't need to fit in memory, but very long videos take longer on slower devices.