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how in the world do you make a multi-line whitelist?

I was going for something like

@@/(ad|track)\.(mp(e?g|3)|wav|avi|swf|class)/

meaning anything with "ad" "track" ending in .mp3, .mpg, .mpeg, .wav, .avi ,swf, and .class wouldn't be blocked.

I think, You are almost right. You just missed a .* for any key between (ad|track) and the file ending.
Also you could add $ at the end, as it stands for End of line.

Then it would be:
@@/(ad|track).*\.(mp(e?g|3)|wav|avi|swf|class)$/