Convert FLV to MP4
Convert FLV to MP4 online free: old Flash and stream videos become MP4 that plays on any phone, TV or editor. Many at once, nothing is uploaded. No sign-up.
FLV
FLV is the Flash Video format: YouTube, game streams and video sites used it until Flash ended in 2020, and some stream recorders still write it.
Newer FLV files hold H.264 and AAC and can be remuxed to MP4 in seconds; FLVs from the 2000s use Sorenson Spark or VP6 and are re-encoded.
FLV to MP4: remux or re-encode
Some FLV files are remuxed into MP4 in seconds, without quality loss; older ones with codecs MP4 can’t hold are re-encoded. The list shows which way each file goes before you start.
A remuxed file is about the same size as the FLV. A re-encode, or the High, Balanced and Small presets, makes it smaller: a 1080p minute is around 45 MB at High and 30 MB at Balanced.
How it works
- Drop one or more FLV files: MP4 is already selected. Quality, maximum resolution and sound can be changed before you start.
- Streams that fit MP4 are copied; anything else is re-encoded with WebCodecs, or FFmpeg compiled to WebAssembly when the browser can’t.
- Download each file, or all of them as one ZIP.
Questions
Are my videos uploaded?
No. Reading, remuxing and encoding all run in this browser tab. Open DevTools and watch the Network tab while a file converts: no request carries it.
Why is one file done in seconds and another takes minutes?
A remux only copies the streams, so it runs at disk speed. A re-encode decodes and encodes every frame; FFmpeg in WebAssembly, used when the browser can’t, is slower still.
How large can a video be?
Up to 3 GB per file for free, and as many files as you like. Remuxes and WebCodecs re-encodes stream from the disk; the FFmpeg path holds the result in memory.