ASF, Advanced Systems Format File (.asf)
The ASF Video file format
ASF is the digital audio and video container format from Microsoft and has been known as Active Streaming Format or Advanced Streaming Format. It is designed for the streaming of audio-visual content. The file containers for streaming media, Windows Media Video, and/or Windows Media Audio are contained within ASF files. This file type often contains WMA and WMV files. WMV and WMA files are nearly identical to ASF files, save for the extension name and MIME-type. The replacement of ASF took place to ease identification between video and audio files. In 2000, VirtualDub described ASF as “a poor man’s AVI,” commenting on the simplicity and “poorly-designed” aspects of the format. Though not popular, it is still a very usable file format.
Technical details of ASF files
Much like MP3 files, files with the ASF extension can contain metadata including artist and album name, release date, length, year released, genre, etc. Streaming is possible assuming the correct amount of data has been downloaded before attempting since the file continues to download while watching (like on YouTube, for example). Because of the streaming capabilities, the maximum resolution maxes out at 352x288. ASF files are created to support playback from digital media serves, HTTP servers, and storage devices. These files use a combination of the following: elliptic curve cryptography key exchange, DES, custom block and RC4 stream cipher, and SHA-1 hashing functions. ASF has all but been replaced by WMA and WMV files.