Specifically, I am asking about TED talks. They are available for sharing and downloading freely. Is it also true about their transcripts?
The usage policy page is unclear about that, because they do not clearly state exactly what "TED Talks" refers to, so you might think that it refers to the videos and the transcripts. However, their explanation of the license attributes suggests that the license only applies to the videos. Under "Attribution" they say "TED's logos within the videos and visuals as well as those of the TED Talks sponsors remain untouched and unedited," which could not be the case of a transcript. Under ND, they say "You cannot alter the videos in any way. This means you cannot edit, remix, cut, shorten, add overlays to them, or, well, alter them in any way", which indicates that they only intend the videos to be available under the CC license, and under repost/republish they say "You must use the TED embeddable player. This allows us to further our overall mission by tracking video usage. Scraping video from TED.com is not permitted", which again implies that only the videos are licensed. The totality of their wording is directed at the videos and there is hardly any recognition that there are transcripts. In lieu of any separate license for transcripts, one should conclude that they are not licensed.