What is an FLV file?

FLV is a container: a wrapper that holds streams encoded by something else. It is used for streaming.

The extension is .flv, and the full name is Flash Video. Both matter less than what the file can hold, which is what the rest of this page is about.

Adobe published it in 2002.

Age is worth knowing here for one practical reason: the older a format is, the more programs have had time to learn it.

It is written down and implementable, though the vendor decides what the next version looks like. In practice that is enough for the file to keep opening; it is not enough to be sure of it.

The people who made it have moved on, and support is being withdrawn rather than added. Anything still in this format is worth moving while the tools to move it are still around.

It usually holds H.264 and Sorenson Spark. This is the distinction behind most "why will this not play" questions: two files with the same extension can contain entirely different encodings, and a player that refuses one may be perfectly happy with the other.

It also explains why changing container is often fast and lossless while changing codec is neither. Moving the same stream into a different box rewrites the box; re-encoding rewrites the picture.

FLV can hold a layout that lets it start playing before it has finished arriving.

That matters mostly when converting: whatever the target cannot hold is dropped, usually without a warning.

VLC and FFmpeg read it, and so do most programs of the same kind.

If a file will not open, the format is rarely the problem — it is more often that the program predates it. Converting to something older is the reliable way past that, and it is what the rest of this site is for.

No browser reads it.

That is the single most common reason to convert it: not that the format is bad, but that the place you want to show the file cannot read it.

FLV is meant to be handed over rather than worked in. Editing one is possible and rarely pleasant; the sane approach is to change the source and export again.

The recurring complaints: support outside its home ground is uneven.

None of these is a reason to avoid the format. They are the things worth knowing before you are surprised by one, which is a different claim and a more useful one.

Adobe announced in 2017 that Flash would reach end of life, and on 31 December 2020 it did. Browsers removed the plugin, Adobe added a kill switch that blocks remaining installations from running content, and the runtime that played FLV files simply stopped existing.

That makes FLV unusual. AVI and MPEG-2 are old formats with declining support; FLV is a format whose playback was ended on a published date by the company that owned it. Anyone holding one has a file stranded by a decision rather than by neglect.

Before 2005 there was no way to put video on a web page that worked reliably across browsers. Each had its own plugin — QuickTime, RealPlayer, Windows Media — and none was universal. Flash was already installed nearly everywhere for animation, so putting video inside it solved the problem overnight.

YouTube launched on FLV. So did Vimeo, and for most of a decade essentially all web video was Flash video. The format was not technically remarkable; it was the one that could actually reach an audience, which is the same argument that keeps MP4 dominant now.

Early files hold Sorenson Spark, a variant of H.263, and they look it — soft, blocky in motion, capped at low resolutions. Later ones hold VP6, which was noticeably better. From about 2008 onward FLV increasingly carried H.264, which is the same codec MP4 uses today.

That last group is the good news for anyone converting. If the file dates from the later years, the video inside is modern and can be repackaged into an MP4 without re-encoding — the streams are copied and nothing is lost. Earlier files genuinely have to be re-encoded, and no amount of care will recover detail Sorenson Spark discarded in 2006.

Adobe introduced F4V alongside FLV when H.264 support arrived. Confusingly it is not a variant of FLV at all — it is essentially MP4, using the same underlying structure, with an Adobe extension.

So an `.f4v` frequently plays if renamed to `.mp4`, and converting one is usually trivial. If you have a folder of Flash-era video, sorting it by extension is worth doing first: the F4V files are likely to need nothing more than repackaging.

Downloaded web video from before 2012, which is the largest group by far. Screen recordings made with Camtasia and similar tools, which defaulted to FLV for years. E-learning packages and corporate training modules, which were built in Flash and stored their video this way. Recordings from webinar platforms of the era. And archives from sites that have since shut down.

The common thread is that the content is often not available anywhere else. A training module or a webinar recording from 2009 is usually the only copy, which makes conversion an archival job rather than a convenience.

FLV stores its metadata — duration, dimensions, frame rate — in a tag that streaming tools frequently wrote at the end of the file or omitted entirely, because a live stream does not know its own length while it is happening.

The result is a file that plays but reports no duration, shows a seek bar that does not work, or claims a length that is plainly wrong. It is not damage. Converting to MP4 fixes it as a side effect, because the new file gets a proper index written after the content is known.

No subtitle track, no chapters, no orientation flag, and no place for the metadata a camera or an editor would write. Flash applications that showed captions did so with the player’s own code reading a separate file, and that code is gone along with the runtime.

So if a training video had captions, they were almost certainly in the surrounding Flash project rather than in the FLV. Converting the video will not produce them, and recovering them means finding the original package rather than examining the video file.

MP4 with H.264 is the destination, and how long it takes depends entirely on what is inside. A later FLV already holding H.264 can be repackaged in seconds with no quality change. An earlier one holding Sorenson Spark or VP6 must be decoded and re-encoded, and takes real time.

For the re-encode, choose a generous quality setting. The source is already a low-resolution file from a weak codec and there is nothing to save by being frugal — the goal is to lose nothing further, not to make the file small. Upscaling it will not help; the detail was never recorded.

Because this content is usually irreplaceable, treat the conversion as making an access copy rather than replacing the file. Storage is cheap, the original FLV is small by modern standards, and there is no way to go back if the conversion settings turn out to have been wrong.

There is no FLV conversion on this site to do it with, which is why this page lists none. Sorenson Spark and VP6 have no browser decoder at all, and nothing here reads the container even when the video inside it is already H.264, so the pairs are declared and waiting on a server-side ffmpeg build. A folder of two hundred training recordings is a batch job for VLC or HandBrake on the desktop today — both of which do the work on your own machine rather than moving every file across a network to do it.