I've heard that some lecturers like to write on the board a lot, which doesn't get put online, though. I'm guessing that doesn't happen often?
I'm probably gonna have the same problem! Notes notes notes. Thank god for recorded lectures. I can imagine it already... Going to every single lecture, then realising I'm gonna have to rewatch it all at home anyway...
How long do the lectures stay online? Forever?
I found that the maths lectures were hard to watch online because some streams would use the white/blackboards and it wouldn't be recorded. But I found maths stuff to be better paced in the lectures.
Biology and chem all run off slides that are recorded with audio so they are fine.
Definitely go to the first few lectures and check how the recordings turn out. Also remember you take the risk that there could be an error with the recording.
They stay online for the full semester until the subject is removed from your LMS page.