Advanced streaming format
ASF Description
Advanced ( formerly Active ) Streaming Format was developed by Microsoft in 1995-1998. Its main purpose is to serve as an universal format for storing and streaming media. There are two versions of ASF. Version that is known as 2.0 is well-documented and its specifications are publicly available. Unfortunately, they are not very helpful for developers because this format is not widely used ( if used at all ).
On the other hand, there's another version of ASF format ( 1.0 ). It is extremely popular. All files with extensions .asf, .asx, .wmv and .wma that you can find in the 'Net are stored in ASF 1.0. Microsoft never released any documentation covering this format. There's a rumour that this format is even patented! This situation similar to the one with MPEG-4 specifications: Microsoft appears to take active part in development of specifications for MPEG-4 but does not use these formats in its products, instead, it promotes their closed-source variations DivX ;-) and Windows Media Video ).
As long as Microsoft does not provide implementations of ASF reader or writer for any platforms except Windows and Macintosh, it is necessary to have at least minimal specification of the format to implement tools for working with ASF 1.0 on all other platforms. This document tries to organize all available information covering the format, received from different sources.
Readers are encouraged to get acquainted with ASF 2.0 specifications to better understand the ideas beyond the format and other features that it offers.
ASF (Advanced Streaming Format) is a file format that stores audio and video information and is specially designed to run over networks like the Internet. It is a highly flexible and compressed format that contains streaming audio, video, slide shows, and synchronized events. ASF enables content to be delivered to you as a continuous flow of data with little wait time before playback begins. This means that you no longer have to wait for your audio and video files to fully download before starting to view them. You simply launch the Windows® Media Player and begin. For example, you can spend more than 40 minutes to download an uncompressed AVI file that's 40 seconds long over a 28.8 Kbps modem, and that requires 1.5 Mbps in bandwidth to play it back. It would be virtually impossible to deliver training presentations that run approximately 20 minutes each segment. When that AVI file is compressed and converted to ASF, it begins playing after only a few seconds. The file can be of virtually unlimited length, and can run over Internet bandwidths. |
