All about ASF files

ASF stands for Advanced Systems Format and is Microsoft's proprietary container format for audio and video files. The format was developed between 1996 and 1998, originally under the name Advanced Streaming Format. The name also reveals its main purpose: streaming over the Internet.

Like MP4 or MKV, ASF is also a container that can hold various codecs. In practice, ASF files almost always contain Windows Media Video (WMV) or Windows Media Audio (WMA). Therefore, the file extensions .asf, .WMA, and .WMV are often used synonymously.

Technical features

ASF was very advanced for its time. The format supports progressive streaming, which means that a file can start playing before it has been completely downloaded. Multiple audio streams (for different languages or bandwidths) are also possible. In addition, ASF already supports DRM (Digital Rights Management), which means that some ASF files can only be played on authorised devices.

Last updated on 11. March 2026 by Sören with the experience of more than 127,898,492 converted files since 2013.