Why won't the video start playing? Is it broken?

This is a tricky problem on the site, but it's not our fault. Because the videos (and audio) are provided by someone else, we are at the mercy of whatever process they used to create the files. Without getting too technical, I will explain it like this:

Audio and video files are encoded using a codec. Basically, it is a way to tell your computer how all the information is put together. Some audio and video codecs have all the information about how to play the file at the very end of the file, so your computer has to wait until it has loaded the entire file before it can start playing. This isn't a problem if the file is sitting on your hard drive, but it's bad news if you are trying to watch the video over the Internet. In these cases, your computer has to download the entire file (sometimes several hundred megabytes!) before it can start playing even the first few seconds of the file.

In other words, please be patient. Even if you are on a fast connection, it may take several minutes before the file can be downloaded. Slower connections can take significantly longer. We know that this is an aggravation for you, and we're trying to figure out a way around it. For now, just consider it to be a minor inconvenience in the world of free education.