FLV to MKV converter
Convert FLV to MKV in seconds, free and unlimited. No upload, no sign-up, no watermark: your video never leaves your device.
Last updated
Quick answer: To convert FLV to MKV, add the FLV file to the iHateFiles FLV to MKV converter and press Convert. The conversion runs in your browser, so the file is never uploaded, and it is free with no sign-up, watermark or size limit. Re-encodes the picture and sound into a MKV container.
Should you convert FLV to MKV?
Do this when something specifically needs MKV. The picture is re-encoded, so it costs a little quality; if all you need is a file that plays everywhere, MP4 is usually the better target.
The picture is re-encoded
An FLV usually holds Sorenson Spark, VP6 or H.264 from the Flash era. This writes H.264 video with AAC sound into the MKV. Both sides are compressed with loss, so this is a second generation: leave the quality at its default or higher, because the encoder is working from FLV artefacts rather than the original.
Expect a smaller MKV
H.264 video is a much more efficient codec than what an FLV holds, so at the same visual quality the MKV is usually a third to a half of the size.
Where the MKV will play
MKV plays on VLC, Plex, most smart TVs and Android, but not the iPhone Photos app or QuickTime.
FLV and MKV side by side
| FLV | MKV | |
|---|---|---|
| Inside the file | Sorenson Spark, VP6 or H.264 from the Flash era | H.264 video with AAC sound |
| Compression | Lossy | Lossy |
| Carries sound | Yes | Yes |
| Plays on | VLC and very little else since Flash was retired in 2020 | VLC, Plex, most smart TVs and Android, but not the iPhone Photos app or QuickTime |
| Here | Read and write | Read and write |
What usually goes wrong
About the FLV. If you have FLV files they are probably old downloads worth rescuing, and converting them to MP4 is the way to keep them watchable.
About the MKV. MKV and WEBM share a signature because WEBM is a restricted Matroska, so tools sometimes report one as the other. What matters is the codecs inside.
How to convert FLV to MKV
- Add your FLV file. It is read from your disk and stays there.
- Check the settings. The output format is already set to MKV.
- Press convert and the MKV file is saved back to your device.
Questions
How do I convert FLV to MKV?
Open this page, add your FLV file, and press convert. The file is decoded and re-encoded by your own browser and saved back to your device. Nothing is uploaded.
Is this FLV to MKV converter free?
Yes, completely. There is no account, no sign-in, no watermark and no daily limit, because there is no server doing the work. Your own device does it.
Are my files uploaded anywhere?
No. There is no upload endpoint. The conversion runs inside this browser tab, so your file never leaves your device. You can open your browser's network panel and watch: nothing carrying your file is sent.
Is there a file size limit?
No fixed limit. Because the work happens on your machine there is no server quota. The only ceiling is your own device's memory, which for video means very large files may be slow.
Will converting to MKV lose quality?
MKV is a lossy format, so some detail is discarded. The quality control on this page decides how much. The default is set high enough that most people cannot see the difference.
Can I convert several FLV files at once?
Yes. Add as many as you like and they are converted one after another, then offered as a single ZIP.