Advanced System Format (ASF – formerly Advanced Streaming Format) is Microsoft’s proprietary digital audio / digital video container format especially meant for streaming media. ASF is part of the Windows Media framework. The ASF format does not specify which codec should be used to encode the audio or video – it just specifies the structure of the audio / video stream. This is similar to the QuickTime and AVI container formats. The most common file types contained within the ASF file are Windows Media Audio (WMA) and Windows Media Video (WMV). ASF files can also contain metadata including artist, title, album and genre for an audio track, or director of a video track, similar to ID3 tags of MP3 files.
Find your answers here.