Why do I get the message "Corrupted media encountered during playback” when I try to play a video on my PC? 

The file you are playing is either corrupted or is in a format not supported by RealPlayer.

A file can become corrupted for a variety of reasons. If you originally downloaded the video from the internet, re-download the video and then try to play it again.

For more about unsupported file types, read this article.