captainsolo said:
Is it ProLogic encoded?
Yes, it's a ProLogic encoded track.
Chewtobacca said:
I've never understood how a presumably pure stereo track can become a 2.0 surround track. Where does the matrixed surround sound come from if the source is two channel?
I think it's the name "Dolby Stereo" that confuse you, an optical 35mm Dolby Stereo track isn't just two channels, it's a four channel configuration; Left-Center-Right-Surround.
Chewtobacca said:
I also don't understand why the other mix on the BD is 4.1 and not 5.1. If it comes from a six-channel mix, why is it not 5.1?
hairy_hen described it better than I can do here: http://originaltrilogy.com/forum/topic.cfm/Ultimate-Trilogy-Set/post/567939/#TopicPost567939
Edit: Moth3r beat me to it. ;)