Designing an Effective PowerPoint Presentation: Quick Guide from the OWL: Purdue Online Writng Lab.
APA does not offer specific advice on how to cite within a PowerPoint. But one can assume that a PowerPoint is simply a paper and that all the rules that apply to a paper apply to the PowerPoint. In-text citations (or parenthetical citations) point your viewer to specific entries on the References page.
With that said, general rules must be followed.
Below is a Sample PowerPoint in which APA format is used. Remember that the placement of the parenthetical citation on a slide is not absolute. However, it should be apparent to the viewer where the information is coming from.
In APA a Youtube video is best cited as a video blog post.