Explaining 'this' in Media.call();

You have the idea correct.

function Media(title, duration) {
   this.title = title;
   this.duration = duration;
   this.isPlaying = false;
}

Media here is a constructor function. It allows any number of items to be created and assigns each of those items it's own set of variables title, duration and isPlaying.

function Song(title, artist, duration) {
    Media.call(this, title, duration);
    this.artist = artist;
}

Song is also a constructor function. However because we already have a Media constructor, we can use it similar to how a prototype would work. By using ConstructorName.call we are saying we want to use another function.

.call would be like any other method but, it is designed specifically to allow two functions to work together.

So in this case like you already understood, we don't need a Song constructor repeating the same thing Media does, we can just call it and end up with a Song that has

this.title = title
this.artist = artist
this.duration = duration
this.isPlaying = false

This is similar to how a prototype would work. At anytime, if we want to add something into the Song constructor we could create a prototype that allows you to add something in indirectly.

Song.prototype.yearReleased = function(year) {
     console.log("The song " + this.title + " by " + this.artist + " came out in " + year);
}

and when the prototype is called we can simply call it the same way we would something in the constructor function.

yourSongVariable.yearReleased("1989");