The Flynnlives guy (who was just shot by police) was the one who posted that link, I believe.  And there are several videos like that from different venues.    I have a strong background in related technologies and have no idea how that video happened unless it was a full-on CGI fake.  Though I'm not sure either how a hologram would be good enough to fool people in person.  Unless the "rally", was actually at a sound stage somewhere and the audience were hired shills (like the ones here).