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Remux an MKV into an MP4 in seconds, without re-encoding or losing quality, so it opens in editors, phones and upload forms. It runs in your browser; nothing is uploaded.
Your media is processed in your browser and is not uploaded to our servers for conversion. Page assets (including the converter engine) still load over the network.
Select or drop a video to convert to MP4
MOV, WebM, MKV, AVI, M4V and more. Converted on your device.
Click, tap, or drop a fileChoose the MKV
Drop or select the .mkv file.
Use Fast mode
It's preselected: the video and audio are copied into an MP4 without re-encoding.
Convert
Remuxing is quick even for large recordings, because nothing is re-encoded.
Download
Play the MP4 in the page, then download it.
MKV (Matroska) is popular for recordings because a crash or power cut doesn't corrupt the whole file, which is why OBS Studio users often record to MKV. But many editors, phones, social sites and upload forms only accept MP4.
MKV recordings usually already contain H.264 or HEVC video with AAC audio, which MP4 supports, so no re-encoding is needed: Fast mode copies the streams into an MP4 losslessly. MKV can also hold several audio tracks and subtitles; the MP4 keeps the first video and first audio track.
Fast mode reads the MKV and writes the same video and audio streams into an MP4 container, with the index at the start so it plays immediately. Quality is bit-for-bit identical.
If the MKV contains codecs MP4 players don't support, such as VP9 video or FLAC and Opus audio, Fast mode may produce a file that won't play. Switch to Maximum compatibility to re-encode to H.264 and AAC.
No re-encoding in Fast mode, so the MP4 has exactly the same quality as the MKV.
Up to 500 MB on a computer in Fast mode.
MP4 opens in Premiere, iMovie, DaVinci Resolve, CapCut and phone galleries.
Recordings are remuxed on your device; nothing is uploaded.
No. The conversion runs in your browser with a WebAssembly build of FFmpeg. The video is read from your device and the MP4 is saved back to it.
Not in Fast mode. It copies the existing streams into the MP4 container without re-encoding, so quality is identical.
The first video and first audio track are kept. Additional audio tracks and subtitle tracks are not copied.
Fast copies the existing video and audio into an MP4 without re-encoding, so it takes seconds, keeps the exact quality and handles files up to 500 MB on a computer. Maximum compatibility re-encodes to H.264 and AAC, which play everywhere, but it is slower and works for videos up to 120 MB and 10 minutes on a computer.
Fast mode handles up to 500 MB on a computer and 250 MB on a phone. Maximum compatibility re-encodes every frame in the browser, so it is limited to 120 MB and 10 minutes on a computer, or 60 MB and 5 minutes on a phone. Trim longer videos first.
It does the same job, a lossless container change, without needing OBS installed on the computer you're using.
Related: Video Converter · Trim Video · Compress Video to 25 MB · Remove Audio from Video · All tools