The MIME type video/x-flv is used to denote the presence of Flash Video media files. This MIME type falls under the "video" category.

The Flash Video files carry the extension FLV. This is a container format that used in conjunction with the Adobe Flash Player to deliver video over the Internet. This format has been implemented since version 6 of the Flash Player. Flash was originally developed by Macromedia, which was then bought out by Adobe. FLV files can also be embedded within SWF files. FLV is one of the two different video file formats that are supported by the Flash Player. The other video format is F4V, which is encoded using the ISO base media file format and was first implemented in version 9.

FLV is encoded the same way SWF files are encoded. The FLV format is the dominant format through which embedded and streaming video media is served over the Internet. There are many online services that use this format. The most noteworthy are services like YouTube, Google Video and Yahoo! Video. Since FLV is only a container format, the codecs used within may vary. Hence, even though the FLV format itself is open, the codecs may easily be closed and patented.