.flv File Extension

What kind of file is an .flv?

An .flv file is a Flash Video container. It packages timestamped video, audio, and optional script data rather than specifying one codec. Adobe's format specification allows one video stream and one audio stream, so two FLV files can require different decoders.¹

The conventional media type is video/x-flv. Its x- prefix reflects that it is not registered in IANA's current media-type registry.² A valid file starts with the ASCII characters FLV, or hexadecimal bytes 46 4C 56. The following byte states the FLV version, commonly 01.¹

How do I open an .flv on my computer?

VLC is a practical first choice on Windows, macOS, and Linux. Its published input-format list includes FLV, along with legacy codecs often found inside these files.³ FFmpeg can inspect, decode, remux, or transcode FLV through its FLV demuxer.⁴ Adobe Animate can also import FLV for authoring work.⁵

Current browsers do not generally play standalone FLV through HTML video. Do not reinstall the retired Flash Player to open one. Adobe ended Flash Player support on December 31, 2020 and blocked Flash content beginning January 12, 2021.⁶ On phones and tablets, use a maintained media app that explicitly supports the container and its codecs.

If a file has sound but no picture, or picture but no sound, the container may be intact while one stream uses an unsupported codec. Inspect the streams before assuming that the file is corrupt.

Poly support for .flv

Poly gives decodable FLV videos thumbnails, timeline previews, in-app playback, technical metadata, visual search, searchable speech transcripts, and agent understanding. Metadata can include duration, dimensions, frame rate, codecs, color information, and audio-track details.

Transcript search requires a usable audio track with audible speech. Silent video can still benefit from visual search. A damaged FLV or one containing an unsupported legacy codec may have limited playback, indexing, or agent access.

History of .flv

Macromedia introduced Flash video capabilities with Flash MX and Flash Player 6 in 2002. FLV became a common way to deliver video during the browser-plugin era. Adobe later acquired Macromedia and published the format specification.¹⁷

FLV is distinct from SWF. An .swf file can contain an interactive Flash presentation or application, while .flv stores linear audiovisual media that an SWF could load. F4V is different again: it belongs to the ISO Base Media File Format family used by MP4.¹

Working with .flv and alternatives

For everyday playback and web delivery, MP4 or WebM is usually a better destination.

Remuxing changes the container without recompressing compatible streams. Transcoding decodes and re-encodes them, which can reduce quality. Keep the original until you have checked the converted video's full duration, picture, sound, synchronization, and any metadata you need.