# MKV to MP4 converter: free, in your browser, no upload

> Convert MKV to MP4 in your browser. H.264, HEVC and AAC tracks are copied without re-encoding, so there's no quality loss; anything else is encoded to H.264 and AAC. Nothing is uploaded.

URL: https://cutfac.com/tools/mkv-to-mp4  
Last updated: 2026-10-28  
Language: [한국어](https://cutfac.com/ko/tools/mkv-to-mp4)

Drop in an MKV from OBS or another recorder and get an MP4 that editors, phones and upload pages take. Most MKVs move over without re-encoding, and the file never leaves your browser.

Runs in your browser. Nothing is uploaded.

## How to use it

1. **Add an MKV.** Drop the file. The tool shows which video and audio it holds and what will happen to each.
2. **Convert.** Copied tracks take seconds. Tracks that need encoding take longer, so keep the tab open.
3. **Check and download.** Play the MP4 to check it, then download it.

## Why MKV, and why MP4

MKV is a container that keeps what was written if a recording stops suddenly, which is why OBS recommends it for recording. Many editors, phones and upload pages want MP4 instead.

Both can hold H.264 or HEVC video and AAC audio. When the MKV has those, the tracks move into the MP4 as they are: nothing is decoded or encoded again, so it's quick and the picture is unchanged.

## When it encodes

VP9 or AV1 video is encoded to H.264, and Opus, Vorbis or FLAC audio to AAC, since MP4 players don't all take them. That takes much longer than copying, depending on the video's length and your computer.

Only the main video and audio tracks are kept: subtitles, chapters and extra audio tracks are left out. AC-3 and DTS surround audio can't be decoded in most browsers; use ffmpeg for those files.

## In OBS or with ffmpeg

OBS has File > Remux Recordings, and an option in Settings > Advanced to remux every recording to MP4 when it stops. On the command line, this copies the first video and audio tracks:

- ffmpeg -i input.mkv -map 0:v:0 -map 0:a:0? -c copy output.mp4

## Sources

- [OBS Knowledge Base: Standard recording output guide](https://obsproject.com/kb/standard-recording-output-guide)
- [FFmpeg documentation](https://ffmpeg.org/ffmpeg.html)

## Questions

### Is my video uploaded?

No. The MKV is read and the MP4 is written in your browser. Nothing is sent anywhere.

### Does converting MKV to MP4 lose quality?

Not when the tracks are copied, which is the case for H.264 or HEVC video with AAC audio, as most OBS recordings have. Only tracks that need encoding are re-compressed, at high quality.

### What happens to subtitles and extra audio tracks?

They're left out. The MP4 keeps the main video and audio track. Use ffmpeg if you need the others.

### Why does it say the video couldn't be converted?

Usually the audio is AC-3 or DTS, which most browsers can't decode; the tool stops rather than make an MP4 without sound. Try Chrome, or use the ffmpeg command in the guide above.

### How big a file can I convert?

The MP4 is built in your browser's memory, so a recording of several gigabytes may not fit. For those, use OBS's remux or ffmpeg.