FLV to MP4 — in your browser

FLV, briefly

FLV (Flash Video) was Adobe's container format for web video, dominant from 2002 to roughly 2015. Inside is typically H.264 (or older Sorenson Spark / VP6) video and MP3 or AAC audio. The container is the only part that's outdated; modern FLV files usually contain H.264 + AAC which transfer cleanly to MP4 without re-encoding.

Where you still find FLV files

• Old downloaded videos archived from the 2000s.
• Twitch VODs (the legacy ones — new ones are MP4).
• Stream captures from RTMP via OBS's older "Save to FLV" option.
• Old e-learning material burned to FLV by enterprise LMS systems.

Remux when you can, re-encode when you must

If the FLV has H.264 + AAC inside, remux is instant and lossless. If it has older Sorenson / VP6 video, we have to re-encode to H.264 because MP4 won't accept those codecs. The tool tries remux first.

Why you still have FLV files

FLV was the format of Flash video — the container behind almost all web video from roughly 2005 to 2015, and the standard output of screen recorders and stream archivers of that era. Flash itself reached end of life at the end of 2020, and browser support went with it, so an FLV file today is usually an archive: a downloaded lecture, an old stream recording, a camera capture nobody converted at the time.

The good news is that the video inside a modern-era FLV is very often already H.264, which is exactly what MP4 wants. Where that is the case the conversion is quick and loses nothing.

What happens to the file

The stream is put into an MP4 container with H.264 video and AAC audio. Nothing else about the recording changes — resolution, frame rate and duration all stay as they were. FLV files from the Flash era are often low resolution by today's standards, and converting cannot change that; it makes them playable, not sharper.

If the result is bigger than you want, compress it afterwards. For other formats from the same era, see WMV to MP4 and AVI to MP4.

Related tools

• WMV to MP4
• AVI to MP4
• OBS MKV to MP4
• Convert video