prepositions - Shall I use 'at' or 'in' or 'on' with a website?

If I want to say something like

I watch videos at/in/on MIT open courseware.

Shall I use 'at'/'in'/'on'?
More generally, when talking about websites, which one shall I use?

Answer

I suggest you to use "on" because when we are watching something on screen, using "on" is more appropriate.