Microsoft Advanced Streaming Format

• Extensions: asf, wmv
• Company: Microsoft

There are 2 versions of ASF.

1.0, the used and unpublished format.

http://avifile.sourceforge.net/asf-1.0.htm

And 2.0 the published unused format.

http://www.microsoft.com/windows/windowsmedia/format/asfspec.aspx

Data Format

It is not obvious from examining raw ASF data but the files are organized according to the same chunked paradigm that many multimedia container formats use. However, rather than using FourCCs and 32-bit length fields to delimit the chunks, ASF files use 128-bit (16-byte) globally unique indentifiers (GUIDs) and 64-bit lengths.