We recommend that you view the YouTube video clips using full-screen and in high definition (if your internet connection allows this). Make sure your speakers are turned on so that you can hear the narration as well!
Full screen: click on the button at the bottom-right of each video clip:
High Definition: as soon as you start playing the video you will be able to see the current definition at the bottom-right of the screen, which will show a number such as "360p" or "480p". Click on this number and set it to "720p". (If the video does not play smoothly with this setting it may be because your internet connection is too slow, in which case you will need to use one of the lower settings.)