The Advanced Systems File format is developed by Microsoft and is used by Windows Media.

Audio and/or video content compressed by variety of codecs can be stored in an .ASF file and played back with Windows Media Player, streamed with Windows Media Services or packaged with Windows Media Rights Manager.

The extensions .wma and .wmv are used to define a .ASF file that contains content encoded with the Windows Media Audio and/or Windows Media Video codecs.

An .ASF file consist of three parts: The Header object containing information about the file itself, a Data object containing the media streams and the optional Index object, which supports the random access to data within the file.

It supports data delivery over a variety of networks and protocols while still suitable for local playback.