Edit: I was looking for a better version of this video on youtube. I couldn't find one, but I did find this English Agence France-Presse story that answers the question of why they'd release a video like this: https://www.youtube.com/watch?v=M8PgCUap1Vg
I get the impression that the video is from the mainland, not Hong Kong. The device he's strapped in looks like a "tiger chair":
https://www.news.com.au/world/asia/tiger-chair-sick-torture-...
Edit: I was looking for a better version of this video on youtube. I couldn't find one, but I did find this English Agence France-Presse story that answers the question of why they'd release a video like this: https://www.youtube.com/watch?v=M8PgCUap1Vg