ASFView is a program to read an ASF, WMA or WMV file and decode the headers into human-readable descriptions. The three types of file differ only in extension as a convenient way to tell if they will contain video, and are internally identical.
There isn't much to say about this program. Just tell it the file you want to analyse, and out comes a very detailed breakdown of what all the many headers say. A helpful utility when you can't work out why a file can't play. It's written in C, and is simple enough that it will compile on just about any OS. I've released both the source code - public domain rather than GPL, due to legal complications - and a compiled Windows executable.
When I first wrote this, the ASF format was patented - US patent number 6,041,345. That didn't affect me over here in the EU, where software patents are not considered valid, but I still did not want to be in the position of licencing patented technology. For this reason I made the code public domain rather than GPL.
Do not confuse this with the Microsoft ASFView utility. They share a name, but that is all. The two programs perform almost the same function, and as the name follows naturally from the function both ended up with the same name. I'm not sure which was first - ASFView was one of the first programs I wrote, back when I was just learning C. It's old.
To give some idea of what this program does, here is an example analysis of a WMA file.