FLV to MKV Converter
Convert FLV to MKV free — no upload, no signup
To convert FLV to MKV, drop your FLV 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. Repackage FLV into MKV with no re-encoding.
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 FLV to MKV
Add your FLV videos
Drag and drop FLV 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 FLV to MKV?
Archiving old Flash videos in a modern, robust container keeps them playable in media servers and VLC for years.
What happens when you convert FLV to MKV?
Fylo copies the FLV's streams into Matroska, so the conversion is fast and lossless.
How does Fylo convert FLV to MKV?
Fylo reads the FLV 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 FLV and MKV?
FLV (Flash Video) was introduced with Flash Player 6 and 7 in 2002–2003 and became the format behind early YouTube, news sites and video portals. Later FLVs usually contain H.264 video and AAC audio — the same codecs as 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.
Learn more: FLV format guide · MKV format guide
| Property | FLV | MKV |
|---|---|---|
| Developed by | Macromedia / Adobe | Matroska project (open standard) |
| Introduced | 2003 | 2002 |
| Typical video codecs | H.264, Sorenson Spark, VP6 | Any: H.264, HEVC, VP9, AV1… |
| Typical audio codecs | AAC, MP3 | Any: AAC, Opus, FLAC, DTS, AC-3… |
| Plays in web browsers | No (Flash Player ended in 2020) | Partly (Chrome/Edge for some codecs) |
| Compatibility | VLC and some desktop players; RTMP live-streaming tools | VLC, Plex, Kodi, most smart TVs; not iPhone or many editors |
| Best for | Old Flash archives, RTMP streaming workflows | Movies with multiple audio and subtitle tracks |
Frequently asked questions
Is MKV good for archiving?
Yes — it's open, robust and supported by all major media players.
Will the file shrink?
No, the size stays about the same because nothing is re-encoded.
Is my FLV file uploaded to a server?
No. Fylo runs ffmpeg, the same engine used by professional video tools, compiled to WebAssembly inside your browser. Your FLV file is read directly from your device and never sent anywhere.
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