FLV (Flash Video)
The format that put video on the early web, powering YouTube and a generation of streaming sites before HTML5 took over.
| Full name | Flash Video |
| Extension | .flv |
| MIME type | video/x-flv |
| Developer | Macromedia (later Adobe Systems) |
| Released | 2002 (format); Flash Player 7 added direct support in 2003) |
| Type | Video container |
| Video codecs | Sorenson Spark, VP6, H.264 |
| Audio codecs | MP3, AAC, Nellymoser, Speex |
What is a FLV file?
FLV is a video container format created by Macromedia in 2002 to deliver video through the Flash Player plugin. It became the backbone of online video in the mid-2000s, used by YouTube, Hulu, and most major video sites of that era. Today it has been replaced by MP4 and other modern formats, but millions of FLV files still exist in archives.
FLV stands for Flash Video. It is a container format, meaning it wraps video, audio, and metadata together in a single file. The file is made up of a short header followed by a sequence of tagged chunks, each holding a packet of video, audio, or script data. It was designed specifically for streaming over the internet via the RTMP protocol and the Adobe Flash Player plugin.
History
Macromedia introduced Flash Video in 2002 and added direct .flv support to Flash Player 7 in 2003. When Adobe acquired Macromedia in 2005, the format came under Adobe's control and saw wide adoption as YouTube launched that same year using FLV for all video playback. By 2007 Adobe created F4V as a successor based on the MPEG-4 standard, and as HTML5 video spread through the 2010s, FLV fell out of use. Adobe officially ended Flash Player support at the end of 2020.
Container vs codec
An FLV file starts with a three-byte signature ('FLV'), a version byte, and flags indicating whether the file contains audio and video streams. After a header-length field comes a series of tags. Each tag carries a type code (0x08 for audio, 0x09 for video, 0x12 for metadata), a data size, a timestamp, and the payload bytes. A four-byte back-pointer follows each tag so parsers can seek backwards through the file.
What it is used for
- Playing back archived video files originally recorded or downloaded in the Flash era
- Converting old FLV recordings from screen-capture tools like Camtasia or Camstudio
- Preserving historical web video content from platforms that stored FLV archives
- Re-encoding legacy training or lecture videos saved in FLV before uploading to modern platforms
How to open it
Most modern media players, including VLC, can open FLV files directly without any extra plugins. To play FLV in a browser or upload it to a video platform, convert it to MP4 first using a converter like ConvertIntoMP4.
Pros and cons
Strengths
- Small file sizes relative to quality, well-suited to the bandwidth of the early 2000s web
- Supported streaming over RTMP, which allowed seek-without-full-download on early video sites
- Wide historical support: virtually every Flash Player version from 7 onward could play FLV
- Simple tag-based structure makes it straightforward to parse and extract streams
Trade-offs
- Requires the Flash Player plugin, which reached end of life in December 2020 and is no longer maintained
- Not supported natively by any major browser today without a third-party player or conversion
- Limited to older video codecs by default; H.264 support was added late and is now better served by MP4
- No support for modern features like HDR, adaptive bitrate streaming, or subtitles via standard tracks
Convert FLV files
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From FLV
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FLV FAQ
Can I still play FLV files without Flash Player?
Yes. VLC Media Player opens FLV files on Windows, Mac, and Linux without Flash. You can also convert the file to MP4 so it plays in any browser or device.
What is the difference between FLV and F4V?
F4V is Adobe's 2007 successor to FLV. It is based on the MPEG-4 Part 12 container rather than the proprietary FLV structure, which means it handles H.264 video and AAC audio more efficiently. F4V files use the .f4v extension.
Why did YouTube stop using FLV?
YouTube began defaulting to HTML5 video in January 2015. HTML5 allows browsers to play video natively without a plugin, and MP4 with H.264 became the standard container. FLV depended on the Flash Player plugin, which was being phased out across all major browsers.
Is converting FLV to MP4 lossless?
If the FLV contains H.264 video and AAC audio, you can remux it to MP4 without re-encoding, which preserves the original quality exactly. If it uses an older codec like Sorenson Spark or VP6, the video must be re-encoded to H.264, which introduces some quality change.