Free tool · Convert
MP4 to MKV
Convert an MP4 video into the MKV container.
Convert an MP4 file into an MKV (Matroska) container, a flexible format that supports multiple audio tracks and subtitle streams. Since MKV supports the same H.264/AAC codecs as MP4, this is typically a fast, lossless remux.
- Files never leave your device
- Runs entirely in your browser
- Free, no account needed
How to use MP4 to MKV
Two steps, and nothing to install.
Drop your MP4 file
Add the video. It is read locally rather than uploaded.
Download the MKV
Save the result, identical in quality since nothing was re-encoded.
More free tools
Free, private, and no sign-up on any of them.
How this works in your browser
Matroska is a deliberately permissive container, designed to carry essentially any codec alongside any number of audio, subtitle and chapter streams. That flexibility is what makes this conversion trivial: MKV can describe H.264 video and AAC audio without difficulty, so the compressed streams are copied across untouched and only the surrounding structure is rewritten. No decoder or encoder runs, the operation takes seconds regardless of clip length, and the picture in the output is bit-for-bit the picture from the input. What the container gains you is capacity rather than content, since a remux moves what exists rather than creating tracks that were never there.
MP4 to MKV vs. upload-based online tools
| Feature | MP4 to MKV (in-browser) | Upload-based online tools |
|---|---|---|
| File upload required | No - never leaves your device | Yes - file is sent to a server |
| Processing queue | None - starts instantly | Often, especially at peak times |
| Watermark on output | Never | Common on free plans |
| Usage limits | None - free, unlimited use | Often capped per day or file size |
| Works offline once loaded | Yes, for most tools | No - requires a live connection |
| Account required | No | Often, for anything beyond a trial |
Who uses MP4 to MKV
Home media server libraries
Store files in the container Plex, Jellyfin and similar systems are built around.
Archival storage
Keep footage in a flexible container that can accommodate extra tracks added later.
Preparing for multi-track editing
Move into a container that can hold the additional audio or subtitle streams you plan to add.
Frequently asked questions
What it can and cannot do, and what happens to your files.
Does this re-encode my video?
No. MKV supports the same H.264/AAC codecs MP4 uses, so this just repackages the file into a new container.
Why use MKV over MP4?
MKV is popular for archiving and home media servers since it supports multiple audio tracks and subtitles more flexibly than MP4.
Is there any quality loss?
No, since no re-encoding is needed, quality is identical to the source.
Does this add multiple audio tracks or subtitles?
No, and this is worth being clear about. MKV is capable of holding several audio tracks and subtitle streams, but the conversion moves across whatever your MP4 already contained. Adding tracks is a separate editing job, not something a container change performs.
Why do media servers prefer MKV?
Because it can carry almost anything: multiple audio languages, several subtitle formats, chapter markers and codecs MP4 has no provision for. For a home media library that is genuinely useful, which is why Plex, Jellyfin and similar tools are built around it.
Will MKV play on my TV or phone?
Support is much narrower than MP4. Many smart televisions and media players handle MKV, but plenty of phones, browsers and upload forms do not. Convert to MKV for a media server, and keep MP4 for anything you need to share or play casually.
Is my video uploaded anywhere?
No. The remux runs inside your browser tab.
Convert MP4 to MKV - free, no quality loss.
Files never leave your device. No upload, no account, and free for unlimited use.
Also see: MKV to MP4