You can also mute the sound of any video in your browser just clicking with right button on the Google Chrome´s tab where video is playing and manually select the mute option. Actually the method of the tutorial its better option only for people who usually doesnt want play videos with sound so they just activate the one that they want. But in the oposite side, people that usually play videos with sound but time to time want to mute annoying videos, the default Mute tab option of Chrome is better.