Javascript isn't working.

Hey everyone. I want to play the videos (JWPLAYER), with the sound muted. But it's not working.
At first I tried completely in html, like this:

But for some reason the command cute just wouldn't work.
So I checked the JWPLAYER website and it suggested this:


HTML:

JAVACRIPT:

//create Qualtrics.SurveyEngine.QuestionData object

Qualtrics.SurveyEngine.addOnload(function()
{

jwplayer("myDiv").setup({
 "file": "VIDEO-FILE-URL",
 "height": 360,
 "width": 640,
"mute": true,
});
});


But the Java script seems to not do anything.
Does anybody have any advice?
Thanks a lot!