If You Attended the Conference
List all sources at the end of your essay in alphabetical order by the authors’ surnames, on a page headed "References." Give the author’s last name and first initials; the year and month of the presentation; the title; the name and type of conference and its location.
The University of Wisconsin-Madison’s Writer’s Handbook provides this example:
Lindberg, S. M., & Hyde, J. S. (2007, March). Mother-child interactions during mathematics homework: Socialization of gender differentiation? Poster presented at the biennial meeting of the Society for Research on Adolescence, Chicago, IL.
Cite this presentation in your text by placing the authors’ surnames and date in parentheses:
(Lindberg and Hyde, 2007).
If You Got the Information Online
When the source is not the presentation itself but an online abstract from a conference, cite that database directly, notes the Wisconsin handbook, which provides this example:
Seibel, R., & Saffran, J. (2006, June). Tune or text: The effect of text on melody recognition. Paper presented at the annual meeting of XVth Biennial International Conference on Infant Studies, Kyoto, Japan. Abstract retrieved from http://www.allacademic.com/meta/p94581_index.html
If you watched the presentation as an online video, give the author, date and title as usual, and then provide the URL for the video site, according to the Purdue Online Writing Lab:
Bakker, R.T. (2014). 2013 St Clair County Community College STEM Conference Keynote Presentation. Retrieved from https://www.youtube.com/watch?v=4lSAD_LyeFs
In both cases, the in-text citation is the same, requiring only the authors’ surnames and the year:
(Seibel and Saffran, 2006) or (Bakker, 2014).