To cite/reference a video, give the uploader as the author, even if they did not create it or perform in it. If the uploader has a full name, give that, or else the username.

Reference:

Guy's and St Thomas' NHS Foundation Trust [GSTTnhs]. (2014, March 28). Barbara, the whole story [Video]. YouTube. https://www.youtube.com/watch?v=DtA2sMAjU_Y

Citation:

(Guy's and St Thomas' NHS Foundation Trust, 2014), or if you have quoted from the video, (Guy's and St Thomas' NHS Foundation Trust, 2014, 2:41) i.e. 2 minutes and 41 seconds in