Timer. Intervals with beeps every 15 seconds.
This video is around 30 minutes long, starts with a 10 second countdown to get ready and then continues with intervals marked by a beep sound every 15 seconds while a video of moving flashes of lights in the darkness is played in the background.
It can be used to time a variety of activities: Work out or exercise routine, breathing exercises, stretch routine, practice sport skills, practice reaction time, build a routine with certain steps to follow, speed up your cooking (why not?) and whatever you can imagine.
Check out the channel for other time intervals and versions of the same interval.
