Music on Hold: Application in online documentation not there

The online documentation states

“This example uses a scirpt created in /usr/sbin/ called “ast-playlinein” and it is used to control the parameters of “arecord” which is the program doing the heavy lifting here. Pointing at the script was all that was needed”

I can’t find the script ast-playlinein

That is an example of using it. Google for ast-playlinein and see what you find. Google is your friend.