The .F4F extension belongs to the files of the type, Flash Video Fragment files. These are part files created by the Adobe media flash server and often used by the client player application.

The file is generally a part file, which upon completion becomes a digital flash .flv file. This type of file is generally used to fragment larger sets of flash videos in case of web streaming. According to Adobe's specification, this file format was developed on the Open MPEG standard 12. The F4F file format also provides the feature of audio and video synchronization in case of part FLV video streams.