Why can I hear the audio but not see the video?

This occurs when the speed of your Internet connection is lower than the bit rate of the video clip you are watching and can be caused by either  (a) Internet traffic congestion reduces the speed of your connection below what it should be (for example, you have a high speed DSL or cable modem connection to the Internet, but due to Internet congestion or shared usage, the effective speed of your Internet connection is actually closer to a 56kbs dial up connection).