On YouTube there is a bit of code in the stream player that displays: connection speed, network activity, buffer health, latency, etc. (as in the picture).

Where can I download this little display or how to write the code to imbed it in my video stream player?

Any information on where to look for something like this. 

 

This information comes from certain events or functions, for example:

https://developer.mozilla.org/en-US/docs/Web/Guide/Events/Media_events

https://developer.mozilla.org/en-US/docs/Web/API/VideoPlaybackQuality