The body language interpretations on the "Bombard's Body Language" channel are interesting, but the overall credibility meter dropped when I read the title of her post, "Body Language: Las Vegas (Antifa?) Shooting"
I hope we're not going there.
The comments are most dismaying.
Now with regard to muzzle flashes, in this YT video by "HighImpactFlix," at 3:30 a camera is trained on the stage, with the Mandalay Bay nicely framed behind it, with what seems like a straight-on angle to the purported shooting windows (see my earlier comments about angle of view). Plus, the shots of the stage are pretty steady as these things go, and focus is decent. At about 3:45, the first single shots—or firecrackers, as some attendees have said—are heard clearly. No flashes from the Mandaly windows, but the reports sound more like a small .22 round to me (or a firecracker?), and much nearer to the camera than the Mandalay building.
(Unlike the Marine husband at the Bellagio, who may have some credibility, I have no serious training or experience in distinguishing the sounds of various firearms, but over the years have fired 1,000s of .22 rifle rounds [think gravel pits & Boy Scout ranges] and can easily distinguish one from, say, a shotgun blast ["blast" is the giveaway].)
Then at about 4:20, the first rapid-fire shots are heard, and I see no flickers, no flashes, no blinks in the Mandalay windows.
So, I am indeed now wondering if those rapid-fire 'machine gun' sounds came from those windows at all.
And it's news to me that there was at least one helicopter in the air nearby, possibly coming or going from the nearby heliport.