If it's an international release, I'm sure they'll do a PAL conversion to NTSC for the U.S.
As far as Regional Codes, Region 4 is Australia, since you asked.
For HD, there is no NTSC or PAL, it's all the same, so no video conversion is necessary. And there are only 3 regions total for coding. Australia is Region B. U.S. is Region A.
(Region A is shared by North, Central, and South America, plus a large portion of the Asian market, which is why you can by Japanese Blu-ray Discs and they will play just fine on your American BD players.)
"Jaws is the Citizen Kane of movies."
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