Slipping sales means sales are falling off. He asks what! Because he is talking about old technology ( celluloid film)... And we would be surprised as readers to know it was still in use. That's right.. Is the answer to the unspoken question in his readers minds- why celluloid film? He is saying that's right! Celluloid film is actually in use! Surprise! Surprise! All this is inferred from what he actually writes...it is like there is a dialogue going on between him and his readers.

1.slipping sales Slipping means a status when you stand, for instance, on ice or wet road, you can easily slide and lose your balance, or probably fall off with your upper body going backwards, because of this. so slipping sales mean the sales dropping,sliding, in other words, the sales become worse. 2."That's right", One person said "what?' , which indicates this person's surprise or disbelief, and another person replied ' that's right', this person tried to confirm his previous statement to assure its truth. Hope it can be helpful of somewhat.

"Slipping sales" means fewer and fewer sales. From listening to the audio, the meaning of "that's right" is "it's true". Now I think of it, this is a fairly common interjection (even if there's no-one else around to say "what?").