Convert FLV to MP4 Online — No Upload, No Watermark
FLV is the Flash video container — obsolete in modern browsers and blocked by most platforms. Converting to MP4 gives you a file that plays on every phone, browser, and editor without re-encoding at playback time.
Drag & drop your video here, or click to browse
Max file size: ~2 GB (memory permitting)
Where FLV files come from
FLV was the format of Flash video, so it is what web video looked like from roughly 2005 until Flash was retired at the end of 2020. Files that remain are downloaded lectures, archived webinars, old screencasts, and recordings from streaming software of that era.
What changes when you convert FLV to MP4
| Container | Rewritten to MP4 with the moov atom at the front, so it starts playing before it finishes downloading |
|---|---|
| Video | Re-encoded to H.264 at CRF 23, which is visually lossless for most footage |
| Audio | Re-encoded to AAC, the codec MP4 players expect |
Worth knowing first
Most later FLV files already hold H.264 video and AAC audio; only the container is obsolete. The picture quality you get is bounded by the original encode, which was usually made for slow connections. Converting makes the file playable again but will not rescue a 360p source.
FAQ
Does anything still play FLV?
Desktop players like VLC and MPV do, because they bundle their own decoders. Nothing else does. No browser, phone, smart TV or editor will open an FLV, since Flash was removed from every platform at the end of 2020. Converting is how these archives stay usable.
The FLV already contains H.264. Is re-encoding wasteful?
Slightly, and it is the honest trade-off here. A pure remux would keep the original stream untouched, but the file also has to cope with the odd timestamps FLV often carries. Re-encoding at CRF 23 normalises that and costs very little visible quality.
What about F4V files?
F4V was Adobe's later MP4-based container and behaves like an MP4. Rename it to .mp4 first and it will usually play without any conversion at all.
Is this FLV to MP4 converter really free and without upload?
Yes. The tool runs entirely in your browser using FFmpeg compiled to WebAssembly. Your FLV file never leaves your device — open the DevTools Network tab to verify zero uploads. No signup and no watermark. The practical size limit is the memory your browser gives this tab, which is generous on a computer and a few hundred megabytes on a phone.