Turn FLV files into MP4
Drop in an FLV and get an MP4 back. FLV is leftover Flash video from the era before HTML5 players. The practical difference is that the result opens anywhere, which FLV files do not. Your file never leaves your computer.
Need the other direction? Convert MP4 to FLV
How to convert FLV to MP4
- 1 Drop your FLV .flv or .f4v file onto the page, or click to browse for it.
- 2 Set the quality, or leave the default, which keeps the file small without anything showing.
- 3 Convert. The work happens on your own machine, so how long it takes depends on your computer and the file.
- 4 Download the MP4, or add more files and do the whole set in one go.
Why convert FLV to MP4
- An FLV will not open in a browser, so anything going onto a web page, into a document or into a message has to become an MP4 first.
- Plays on effectively every device, browser and TV made this century.
- Plays without draining the battery, because devices handle it natively.
- Video for the web, social platforms and messaging apps.
- FLV: limited in what it can hold, with no modern features.
FLV compared with MP4
How the two formats differ on the things that decide whether a conversion is worth making.
| Property | FLV | MP4 |
|---|---|---|
| File extension | .flv | .mp4 |
| Browser support | No browser support | Every browser |
| Introduced | 2002 | 2001 |
| Developed by | Adobe / Macromedia | ISO/IEC MPEG |
| Standard | Proprietary | Open |
Quality and what changes
Both formats are lossy, so this is a second generation of compression: the FLV is decoded back to pixels that already carry its artefacts, and MP4 then compresses that. The damage compounds rather than cancelling out, which is why repeated round trips visibly degrade an image. Encode at a higher quality than the source used, and convert once from the best copy you have rather than from an already converted file.
- One MP4 limitation to keep in mind: fussy about subtitle tracks and unusual audio tracks.
Questions about FLV to MP4
Will converting FLV to MP4 lose quality?
A little. Both formats are lossy, so the file is decoded and compressed a second time and the two sets of artefacts add up. At a high quality setting the difference is hard to see, but avoid repeated round trips between lossy formats.
Is my FLV file uploaded anywhere?
No. The whole thing runs inside the browser tab you already have open. Your FLV is read straight from your own disk, converted on your machine and handed back as an MP4. Nothing is sent anywhere, nothing is stored and there is no account.
Is there a file size limit?
There is no server-side limit because no server sees the file. The real ceiling is your device memory, since the input and the output both have to fit in the tab. A few hundred megabytes is usually fine on a desktop machine and considerably less on a phone.
Can I convert several FLV files at once?
Yes. Add as many as you like and they are processed one after another, then offered as separate MP4 downloads or as a single ZIP. Speed depends on your own processor rather than on a queue.
Does the converter work offline?
Yes, after the page has loaded once. The engine is cached by the browser, so you can disconnect, reload and keep converting. That falls out of doing the work locally rather than being a separate mode you switch on.