Is it okay to cite a TED presentation or a video lecture or something similar? If so, how to cite that video for your paper/thesis?
A quick google "apa cite video" would give you lots of advice, such as http://www.easybib.com/guides/citation-guides/apa-format/youtube-video/ which notes:
Last Name, F.M. [Username]. (Year, Month Date). Title of video. [Video File]. Retrieved from URL.
The old-times equivalent of that, to give a reference to a "private communication", was often done and as often heavily frowned upon. Put it in a footnote or in the acknowledgements.