In some case, you may have trouble playing videos. Often, you may see video but not hear sound. More often, you'll hear sound but not hear video. There are many potential causes of this kind of trouble. Occasionally it has to do with our software, and other times it has to do with methods of compression and decompression or CODECs for short. We are not experts on codecs by any means. Here is a list of sites that can help if you run into these kinds of problems. Note that if you open a video up in the Windows Media Player, you should be able to click on File Properties and determine the CODEC used to encode the video. You can also try to play the video in the QuickTime media player. If the video fails to play in either WMP or QT, then there is likely a CODEC issue at hand.

If you learn anything useful, please feel free to add to this thread!
MainConcept - Motion JPEG Codec Software Video Compression
Morgan M-JPEG codec - Video Codec Definitions
All Codecs and Decompressors
Microsoft Codecs