ASF

Advanced Streaming Format is Microsoft's new proprietary audio/video wrapper[?], especially meant for streaming[?]. It doesn't specify how the video or audio should be encoded, but instead just specifies the structure of the video/audio stream. What this means is that ASF files can be encoded with basically any audio/video codec and still would be in ASF format.

Many cases ASF is confused with Microsoft's own implementation of MPEG-4 video format[?], because most of the ASF streams are encoded using this technology.