This (video, specifically) is more likely a codec issue, and perhaps lack of support (or nonexistence of) for hardware accel paths in it on your hardware.
re: posting to a chat I suspect it is routed through sharepoint for good and ill. Different set of tradeoffs. FWIW i've never seen it quite that laggy, but have noticed before.
Posting something to chat while in a meeting will take 5-10 seconds, i have never seen it work instantaneously.