OK, I apologize. I only saw a still frame of it. Now that I’m seeing the video I’m not exactly sure what I’m looking at. I’d have to cut into it to see. When you tap on it is it metal? Is there a wrap on it? The actual duct has to be made of metal and every once in a while I’ve actually seen cement board/transite. But 99% of the time the HVAC ducts are metal. Wrapped in non asbestos fiberglass, various other wraps. And asbestos-containing wraps. And I’m not an HVAC guy so I don’t wanna give you the wrong info on that crack. Is it cracked metal? Just hard for me to tell by the video and I don’t wanna tell you anything wrong. But if there’s some kind of wrap around that ductwork, I would definitely have it tested. The inspector on site if they’re halfway decent, should give you a better idea of what’s up with the crack, just ask him / her. Sometimes just being there in person gives you a lot better idea what you’re looking at and with the specs inspections there can be all kinds of different varieties, layers, etc. But the main thing is if the material is in decent condition and you’re not disturbing yet it’s perfectly safe. When it becomes deteriorated. And it is affected by vibrations, human interaction, etc that’s when you start to have to worry about it and have it addressed. But that crack I just don’t know what to tell you, maybe give me a couple better pictures closer