MKV to MP4, without the wait.
Turn an MKV into an MP4 that plays on iPhones, TVs and editors. The video is copied, not re-encoded, on your device.
How do I convert MKV to MP4 for free?
Drop the MKV into Cutmallow's free converter above. MKV and MP4 are both containers, so when the video inside is H.264 or HEVC (most MKV files) it is copied straight into the MP4 without re-encoding: it takes seconds and every frame is identical. Sound an MP4 can't hold well, like AC-3 or FLAC, becomes AAC. Everything runs in your browser, with no upload, no watermark and no size limit.
Updated
- Output
- MP4
- Video
- Copied
- Speed
- Seconds
- Size limit
- None
How to use it
Drop an MKV (or tap to pick one).
Wait while the video and sound are copied into an MP4.
Save the MP4. On a phone, the share sheet offers Save Video.
How it works
MKV (Matroska) is a flexible container popular for downloads, screen recorders like OBS and TV recordings. An MP4 can hold the same H.264 or HEVC video, so the converter reads the encoded video packets from the MKV and writes them into a new MP4, with the same timing and frame rate. Nothing is decoded, which is why a feature-length file finishes in about the time it takes to read it from disk.
MKV files often carry sound an MP4 player handles badly, such as AC-3 (Dolby Digital) or FLAC. That sound is decoded and re-encoded to AAC at 192 kbps, which every phone, TV and editor plays, and the result screen tells you it happened. DTS and TrueHD sound cannot be decoded by browsers, so files with only that sound cannot be converted here.
It runs on Mediabunny, an open-source media library, in a background thread of the page. Your video never leaves your device.
Tips for a better result
- Recording in OBS? Its MKV recordings convert in seconds: the video is H.264 already.
- MKVs with several languages keep only the first sound track in the MP4.
- Need H.264 for an old TV or editor? Run the MP4 through the compressor with the H.264 format.
Turn it into a Short
Cutmallow's free editor finishes the job. After converting, tap Edit in Cutmallow and your MP4 opens there, still on your device.
- Cuts the pauses and filler words
- Writes animated word-by-word captions
- Exports a 9:16 MP4 for Shorts, Reels and TikTok
Frequently asked questions
Something else? Write to hello@cutmallow.com.
Does converting MKV to MP4 lose quality?
Not for H.264, HEVC, VP9 or AV1 video, which covers almost every MKV: the video is copied exactly. Only sound an MP4 should not carry is re-encoded (to AAC at 192 kbps), and the result screen says when that happens.
How do I convert OBS recordings from MKV to MP4?
Drop the .mkv from your OBS recordings folder into the box above. OBS records H.264 or HEVC video with AAC sound, so both are copied into the MP4 in seconds. OBS also has a Remux Recordings menu that does the same on your computer.
Are subtitles kept?
No. The MP4 holds the main video and the main sound track only; subtitle tracks and extra languages are left out. To burn your own captions into a video, use the free auto captions tool.
Is my video uploaded anywhere?
No. Your video never leaves your device. The file is opened and processed by your own browser, and the result is saved straight from your device.
Is there a file size or length limit?
No. The file is read from your device a piece at a time and the result is written to the browser’s private storage, so long and very large videos work. The only limit is free space on your device.