You can loop videos on the desktop or mobile version of YouTube, regardless of the browser or kind of phone you're using.

Meanwhile, your entire existence (and the existence of any object) can be plotted on what’s called a world line, a curving path through spacetime starting at your birth and ending at your death. A ...

To loop a PowerPoint slideshow, you'll need to enable looping in the program's "Set Up Slide Show" menu.