An ASF file is a media file stored in the Advanced Systems Format (ASF), a proprietary video and audio container format. It contains audio and video data and optional metadata, such as title, author, and copyright bibliographic data. ASF files are developed by Microsoft primarily for streaming media.
ASF files specify the structure of the audio or video stream, but not the encoding method. They often contain Windows Media Audio (.WMA) or Windows Media Video (.WMV) data. They can be compressed using a variety of video codecs.