Sam asked:

<i>So where do the colors come from? What's the encoding from sound to image? Could we have solved this any other way than just changing the file type?</i>

A bitmap image contains a color table and raw information about each pixel as it relates back to the color table.  24-bit bitmaps may be different--if I recall correctly, they store RGB data as three parts between 0-255.

I'm not sure how WMV files are encoded, but I suspect that they use raw bit information as well.  I would have thought that WMV files would be 2 dimensional (time x value) whereas bitmaps are 3 dimensional (x, y, value).  Of course in the wonderful world of computer data, 2D and 3D are easily interchanged.

You might have been able to solve it by looking at the file with a binary file viewer (like Yikes), but without knowing what WMV files look like you probably wouldn't have seen much.  As Eric already said, there's a comment tag at the end of the file that said what program was used to create the file and he went from there.

I'm still a bit surprised that WMV files can be so readily converted to BMPs.