It can happen. Someone sends you a video that you attempt to open and you see a message pop up on your screen that you do not have the right codec to open the video or audio file.
There is a way to find out what the codec is for a video file. Headband.com has a software program called G/Spot.
G/Spot looks at the video file and tells you what kind of video it is, the codec that it uses and other information about the video frame rate and the size of the video file. G/Spot is no wimp, it can identify 719 video codecs and 245 audio codes.
This software is designed for people that understand how to open a Zip file and are willing to fish around for an answer. It is not hard to use but if you don't want to dive into the belly of the beast this is not the software for you.
I would suggest that you only download the program from the primary vendor web site.