Convert MP4 to MKV Online
Turn MP4 files into MKV directly in your browser using ConverterUp. There is no upload, no waiting in a queue, and no account required — your files stay on your device while WebAssembly does the work locally. Adjust quality and dimensions where supported, then download the result. The output keeps the visual fidelity you'd expect from a desktop app while running entirely in the browser tab.
Convert MP4 to MKV nowHow to convert MP4 to MKV
Open the converter
Click the button to open the MP4 to MKV tool. It loads instantly — no install, no signup.
Drop your MP4 file
Drag your MP4 file into the upload area or click to browse. The file stays in your browser memory only.
Download MKV
The conversion runs locally and finishes in seconds. Click download to save the MKV file to your device.
MP4 vs MKV at a glance
Key technical differences between the two formats, so you know what to expect before converting.
| Feature | MP4 | MKV |
|---|---|---|
| Type | Video container | Video container |
| Compression | Lossy | — |
| Audio track | Yes | Yes |
| Common codecs | H.264, H.265, AV1, AAC | H.264, HEVC, VP9, AV1, AAC, Opus, FLAC |
| Browser support | All browsers | Partial |
| Extensions | .mp4 | .mkv |
| MIME type | video/mp4 | video/x-matroska |
| Introduced | 2003 · MPEG (ISO/IEC 14496-14) | 2002 · Matroska |
What changes when you convert MP4 to MKV
- MP4 and MKV are containers. The video and audio streams are re-encoded into codecs that MKV supports (typically H.264, HEVC, VP9), so you get a file that plays reliably rather than a simple rename.
- The audio track is carried over to the MKV file, re-encoded if needed.
- MKV is newer or less widely supported than MP4. Check that the website, app or device where you will use the file accepts MKV.
About MP4
MP4 (MPEG-4 Part 14) is the most widely supported video container. It typically holds H.264 or H.265 video with AAC audio and plays on virtually every phone, browser, TV and editor.
- Best for
- Sharing videos, uploading to social networks and YouTube, and playback on any device.
- Strengths
- Universal playback, good compression, streaming-friendly.
- Limitations
- Lossy codecs, so repeated re-encoding gradually reduces quality.
About MKV
MKV (Matroska) is an open container that can hold almost any video, audio and subtitle codec, with multiple audio tracks, chapters and subtitles in one file.
- Best for
- Movie and TV rips, multi-language videos, archiving with subtitles.
- Strengths
- Extremely flexible, open standard, keeps multiple tracks and subtitles.
- Limitations
- Not playable in Safari or on many phones and TVs without extra apps.
Frequently asked questions
Is the MP4 to MKV conversion really free?
Yes. ConverterUp is fully free, with no signup, no watermarks, and no daily quota for the MP4 to MKV converter. We support the project through unobtrusive ads.
Are my MP4 files uploaded to a server?
No. Conversion runs in your browser using WebAssembly. The MP4 bytes never leave your device, and we have no upload endpoint at all.
What is the maximum file size?
For MP4 input, the soft cap is 50 MB for images and 500 MB for video. Practical performance depends on your device's RAM.
Will the MKV file open everywhere?
Not everywhere. MKV opens in some browsers and players but not all, so check the target app or device first.
Does converting MP4 to MKV keep the sound?
Yes. The audio track is kept and, if necessary, re-encoded into a codec that MKV supports.
Related guide
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