"you're alright, mate?" to a stranger. American equivalent for "mate"
Solution 1:
As an American who's a bit of an Anglophile, I think "Alright, mate?" would be about equivalent to our "How's it going?". It sounds like the person in the video is just practicing saying casual hellos to strangers to help with his social anxiety. Probably saying anything like "hello", "how's it going", "good morning", "good afternoon", even "how do you do" or "howdy" would fit the bill. "Alright, man?" could even work, but would only really be used with actual men, and not women. That might be true for "mate" in England in this context, too, though "mate" is also used for female friends in other contexts. "Man" can be used with strangers in America, not just friends, but you kind of have to be careful how you say it. "Hey, man" might sound offensive to a stranger, depending on your inflection.