MKV to MP4 Converter
Convert MKV to MP4 free — no upload, no signup
To convert MKV to MP4, drop your MKV 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. H.264 MKVs keep their video untouched; only incompatible audio is converted.
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 MKV to MP4
Add your MKV videos
Drag and drop MKV 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 MP4, Fylo repackages the file instead of re-encoding it, with no quality loss.
Convert and download
Click Convert, then download each MP4 file or all of them as one ZIP.
Why convert MKV to MP4?
MKV is great for archives but iPhones, Premiere Pro, WhatsApp and most social networks don't accept it. MP4 makes the same video usable everywhere.
What happens when you convert MKV to MP4?
Most MKVs contain H.264 video, which Fylo copies straight into MP4 — no quality loss and very fast. If the audio is Opus, FLAC, DTS or AC-3, only the audio is converted to AAC. MKVs with VP9 or other codecs are fully re-encoded to H.264. Only the first video and audio track are kept, and subtitles are not carried over.
How does Fylo convert MKV to MP4?
Fylo reads the MKV with ffmpeg compiled to WebAssembly and writes H.264 (x264, constant quality CRF 23) with AAC audio, plus the faststart flag for instant web playback. Most MKV files already contain H.264 video, so Fylo usually copies the video without re-encoding (and converts only the audio if needed), which is fast and lossless. 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 MKV and MP4?
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.
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.
Learn more: MKV format guide · MP4 format guide
| Property | MKV | MP4 |
|---|---|---|
| Developed by | Matroska project (open standard) | MPEG (ISO/IEC 14496-14) |
| Introduced | 2002 | 2001 |
| Typical video codecs | Any: H.264, HEVC, VP9, AV1… | H.264, H.265/HEVC, AV1 |
| Typical audio codecs | Any: AAC, Opus, FLAC, DTS, AC-3… | AAC, MP3 |
| Plays in web browsers | Partly (Chrome/Edge for some codecs) | Yes — every browser |
| Compatibility | VLC, Plex, Kodi, most smart TVs; not iPhone or many editors | Universal: phones, TVs, editors, social media |
| Best for | Movies with multiple audio and subtitle tracks | Sharing, uploading, streaming, editing |
Frequently asked questions
Why is my MKV to MP4 conversion so fast?
Because the video is copied rather than re-encoded — Fylo only rewrites the container (and, if needed, the audio).
What happens to extra audio tracks and subtitles?
MP4 output keeps the first video and first audio track. Extra languages and subtitle tracks are dropped.
Is my MKV file uploaded to a server?
No. Fylo runs ffmpeg, the same engine used by professional video tools, compiled to WebAssembly inside your browser. Your MKV file is read directly from your device and never sent anywhere.
Related tools
Updated