The citation includes the author, year of the original speech and year the video was published, and the time stamp for the beginning of the quotation in place of a page number.
The associated reference is as follows:
Rare Facts [@rarefacts606]. (2017, November 7). I have a dream speech by Martin Luther King Jr HD (subtitled) [Video]. YouTube. https://www.youtube.com/watch?v=vP4iY1TtS3s&t=182s (Original work published 1963)