An F4M file is a data file saved in the Flash Media Manifest (F4M) format. It contains information that describes Adobe HTTP Dynamic Streaming (HDS), Real-Time Messaging Protocol (RTMP), and Real-Time Media Flow Protocol (RTMFP) streams to a video player.

Adobe HDS is used to deliver multi-bitrate audio and video content over HTTP to media players streaming the content. The F4M format was developed to support HDS by describing complex media that may contain several audio language tracks, multiple bitrate renditions, or advanced content protection, to the media players. Although the F4M format was originally designed to support HDS, it has expanded to other transport schemes, such as RTMP and RTMFP. F4M manifest files contain information about the resolution, codec, and availability of multi-bitrate files. F4M files are created by the File Packager tool, which is used for packaging content in Windows and Linux. The tool is available in the Flash Media Server rootinstall/tools/f4fpackager folder. When you package media to be streamed (File Packager only supports .F4V, .MP4, and .FLV files), the content is packaged into .F4F fragment files. The F4M file is also created, along with F4X Index files, in order to accompany the F4F files. Once the media is packaged, it is delivered by Adobe Media Server to client computers streaming the content.