Is my element visible

Use the code sample like this:

if (elFllVsbl ( lyd )){ ...

and not like this:

if (elFllVsbl ( mySound )){ ...

The solution is inspired by an original idea by Bror Arnfast.

Issues:

No sound in Chrome

The Chrome browser will not play the sound. Probably it's a security feature. Automatic playing of sound files are prohibited in the browser, but if you add a button and ask for a click the user can start the sound.

A suggested solution is see this thread on Stackoverflow

If the video is larger than the viewport

Suggested by a student: If the video is larger than the window you could add a div with an id. When the video is visible add the video via JavaScript somewhere convenient.

E.g. a script along these lines:

let srcTag = document.createElement("source");
let video2src = "media/parade-edinburgh-2015.MP4";
srcTag.src = video2src;
document.getElementById('video2').appendChild(srcTag);