Separate music pack given as option during installation, in case people have lots of things on their hard drive and want to save some Mb. And/or also have the music files made into the most compact versions (either .wav or .ram or .flv) and of the least audio quality (which could decrease the file size) as long as it is not noticeable to the common ear. In other words, as long as the music doesn't have statics in it, it's good. I have played with some audio softwares, the very simple ones, and a 2 mb audio file can have the same sound as a 1mb audio file.
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