MP4 to MKV Converter
Convert MP4 to MKV in seconds without re-encoding: every video, audio and subtitle track and the chapters kept, plus your own SRT, ASS or VTT subtitles.
MKV (Matroska) is the open container that media players, Plex, Jellyfin and video editors like for keeping many tracks together: several audio languages, subtitles in any format, chapters and fonts. Changing MP4 into MKV does not need any re-encoding: every stream is copied into the new container in seconds, so quality and size stay the same. You can also add your own SRT, ASS or WebVTT subtitle files with language tags, which MP4 handles poorly. Everything runs in your browser.
How to use this tool
- Choose one or more MP4 files.
- Optionally add subtitle files (or paste subtitles) and type their languages, such as kor, eng.
- Choose whether the first added subtitle shows by default.
- Download the MKV files.
Formula
MKV = the same video + audio streams + subtitles (MP4 text → SRT) + chapters
Video and sound are copied bit for bit. MP4 text subtitles (mov_text) are rewritten as SRT, the subtitle format MKV players support best; added ASS files keep their styling, and WebVTT is turned into SRT. Two kinds of file are re-encoded instead: videos with a rotation flag (MKV players do not reliably rotate, so the picture is turned upright) and AVI/WMV sources, whose frames have no display times.
Example
A 1.4 GB MP4 film with H.264 video, English and Korean AAC tracks and 20 chapters, plus two subtitle files (Korean and English SRT) typed as "kor, eng": the result is a 1.4 GB MKV with 1 video, 2 audio and 2 subtitle tracks, all 20 chapters, and the Korean subtitles on by default.
Frequently asked questions
Does converting MP4 to MKV lose quality?
No. The streams are copied, not re-encoded; only the container changes. The exception is a phone video with a rotation flag, which is re-encoded upright at high quality (CRF 20).
Why would I want MKV instead of MP4?
MKV holds any subtitle format (including styled ASS), any audio codec and attachments, and is the usual format for media servers. MP4 plays on more phones and in browsers, so keep MP4 for sharing.
My subtitles show strange characters. What now?
They are probably an older Korean file in EUC-KR; the tool detects that encoding and saves the track as UTF-8. Other legacy encodings should be saved as UTF-8 first.
Is my video uploaded?
No. The ffmpeg engine (about 30 MB, downloaded once) repackages it inside your browser.
Last updated:
Page address with these inputs: https://kakao.mobile/tools/mp4-to-mkv-converter/
Cite or embed this tool
kakaoCalc. (2026, November 8). MP4 to MKV Converter. https://kakao.mobile/tools/mp4-to-mkv-converter/
“MP4 to MKV Converter.” kakaoCalc, 8 Nov. 2026, kakao.mobile/tools/mp4-to-mkv-converter/.