MP4 to MKV Converter
Convert MP4 to MKV free — no upload, no signup
To convert MP4 to MKV, drop your MP4 video into the box below and click Convert. Fylo converts with ffmpeg running inside your browser, so nothing is uploaded and there's no signup or watermark. MKV accepts every stream as-is, so this conversion is lossless and fast.
Drop videos here
or tap to browse · paste with Ctrl+V · add many at once
Your files never leave your device
If the video already uses codecs that fit the new format, Fylo repackages it instantly with no quality loss.
Advanced
How to convert MP4 to MKV
Add your MP4 videos
Drag and drop MP4 files into the box or tap to choose them. The converter engine (about 31 MB) downloads once, the first time you convert.
Choose quality (optional)
Balanced quality suits most videos. If the codecs already fit MKV, Fylo repackages the file instead of re-encoding it, with no quality loss.
Convert and download
Click Convert, then download each MKV file or all of them as one ZIP.
Why convert MP4 to MKV?
MKV is the container of choice for media servers like Plex, Jellyfin and Kodi, and for archiving videos alongside extra audio or subtitle tracks you plan to add later.
What happens when you convert MP4 to MKV?
Matroska can hold any codec, so Fylo copies the MP4's video and audio streams straight into MKV — no re-encoding, no quality loss, same size. A 200 MB MP4 typically repackages in around 10–20 seconds in your browser.
How does Fylo convert MP4 to MKV?
Fylo reads the MP4 with ffmpeg compiled to WebAssembly and writes a straight copy of every stream — Matroska accepts any codec, so nothing is re-encoded. Every conversion to MKV is a lossless repackage, so it finishes in seconds even for large files. Only the first video and audio track are kept, and the original resolution is preserved unless you pick 1080p, 720p or 480p under Advanced.
What's the difference between MP4 and MKV?
MP4 (MPEG-4 Part 14) is a container format standardised in 2001 and based on Apple's QuickTime file structure. A container holds separately compressed video and audio streams plus metadata such as subtitles, chapters and cover art. Most MP4s use H.264 video and AAC audio; newer files may use H.265 (HEVC) or AV1.
MKV is the Matroska container, an open standard first released in 2002. It can hold virtually any video, audio or subtitle codec, and any number of tracks — so one file can carry several languages, director's commentary and subtitles. WebM is a restricted subset of Matroska.
Learn more: MP4 format guide · MKV format guide
| Property | MP4 | MKV |
|---|---|---|
| Developed by | MPEG (ISO/IEC 14496-14) | Matroska project (open standard) |
| Introduced | 2001 | 2002 |
| Typical video codecs | H.264, H.265/HEVC, AV1 | Any: H.264, HEVC, VP9, AV1… |
| Typical audio codecs | AAC, MP3 | Any: AAC, Opus, FLAC, DTS, AC-3… |
| Plays in web browsers | Yes — every browser | Partly (Chrome/Edge for some codecs) |
| Compatibility | Universal: phones, TVs, editors, social media | VLC, Plex, Kodi, most smart TVs; not iPhone or many editors |
| Best for | Sharing, uploading, streaming, editing | Movies with multiple audio and subtitle tracks |
Frequently asked questions
Does converting MP4 to MKV reduce quality?
No. The streams are copied exactly; only the container changes.
Can iPhones play MKV?
Not in the built-in Photos or TV apps. Keep the MP4 for iPhone playback and use MKV for media servers and archives.
Is my MP4 file uploaded to a server?
No. Fylo runs ffmpeg, the same engine used by professional video tools, compiled to WebAssembly inside your browser. Your MP4 file is read directly from your device and never sent anywhere.
Related tools
Updated