For example a video that is uncompressed could be 500MB+ in size. Using a codec, you can drastically compress this video below 25MB. Depending on the codec and settings used; The video will vary in quality and filesize. Anyone who tries to play this video must have the same codecs installed used to create the video.

You can use a Video Utilities such as afreeCodecVT to determine the Codec of a video. If the codec is properly installed, the video will play just fine.

If your video is choppy, grainy or has distorted images... This is not generally caused by codecs! Ensure you have the latest video drivers installed and you have sufficient hard drive space.