FLV

FLV, short for Flash Video, is a container file format used to deliver digital video and audio over the Internet, historically associated with Adobe Flash Player. Introduced by Macromedia in the early 2000s, FLV became a common format for streaming video on websites and for downloadable clips. The standard file extension is .flv.

An FLV file consists of a sequence of tags that carry audio, video, or metadata. Video codecs used include Sorenson Spark, On2 VP6, and, in later files, H.264. Audio is typically MP3 or AAC. The file starts with a header that indicates the version and the presence of metadata, followed by a stream of data tags containing the actual media data with timestamps. FLV also supports metadata and simple script data tags for cue points.

FLV was widely used for web video and streaming via RTMP (Real-Time Messaging Protocol). YouTube's early videos were distributed in FLV, before moving toward MP4/H.264. The format remains in older content and legacy workflows, but has declined as Flash Player itself was retired in 2020 and as HTML5-based formats like MP4, WebM, and streaming protocols such as HLS and DASH became standard.

Related formats include F4V, a variant that uses an MP4-compatible container to carry H.264 video and AAC audio, and other Flash-based containers. Tools such as FFmpeg, VLC, and various media players can decode FLV files.