What uses ".asf" files?
 

Quicktime doesn't use them, and I tried several other programs. Can someone help me out here?

Windows Media Player (available for macs) can read .asf files. On Macs, I only bother with .mpg files--I got tired of the spam the .asf files usually fire up in Explorer.

ASF is the Microsoft Advanced Systems Format
 

The "official" player for ASF files on Mac OS X is the Microsoft Windows Media Player, available at http://www.microsoft.com/mac/product...er_default.asp . Don't waste your time, it doesn't work. I don't even know why this piece of junk was ever published. Even in the rare case that it opens a file, playback is jerky and choppy and generally terrible.

Instead, download vlc (VideoLan Client) from http://www.videolan.org/vlc/ . It won't open all ASF files in existence, but it does the best job of anything out there. It's being actively developed, it's improving, and it will also play video compressed with codecs that QuickTime does not recognize or has trouble with.

Mark