Okay, I'm getting pretty sick of this.

For YEARS now, my friends and colleagues have emailed me various
little movies (you know, police pursuits, people getting their heads
chopped off, and so on), but many of them fail to run on Windows Media
Player or Real Player because a codec is missing.  Sometimes that's
the end of the story, and sometimes Real Player or WMP attempt to
download something from somewhere, commonly without success.

So a lot of times I'm watching the videos with sound only, and
frequently they fail to play altogether.

My question is:  what exactly are codecs; is there a way I can know
what codec is required to decode a particular video file; and, lastly,
where can I get these codecs?

I'm crossing my fingers there's a magical solution.

Is there a limited number of codecs, so ideally, I can just go to a
website, download them all, stick them in some folder somewhere, and
thereafter all movies will play successfully?  Is the codec something
I myself am supposed to make?

Obviously I have no idea how any of this works.  But it's pretty
infuriating when the guy in the cubicle next to you can laugh his head
off at the latest time-wasting clip, and you're stuck with the
"Windows Media Player is unable to play the file" error message.

Arrghghghghh!  How did he get the codec and I didn't?  We've got the
same company computers, same software, hardware, everything!  Is there
a way I can lift codecs off his machine?!?

Anyhow.  I'm nonplussed.  Would somebody mind giving me the 411 on this situation?

Hi gnossie-ga,
   I have faced the same frustrations with codecs as you are now
facing. Luckily, the solution is reasonably simple. :)
   The word codec stands for COmpressor-DECompressor. It is a piece of
software that is responsible for compressing the audio-video data when
the media file is first created, as well as for decompressing the data
whenever the file is played back. A single video file will usually use
one codec for the audio data and another for the video data. So if you
have just the video codec installed on your system you will only be
able to see the video - no audio data will be available, and vice
versa.
   There are innumerable codecs available (some free and some
commercial), but luckily for you, you will usually not need most of
them. Some are outdated, some are used only by niche applications.
There are only a handful of audio and video codecs that are in common
use. Some codecs will come installed with your operating system, while
others may be installed by software such as games, media players and
audio/video editing software that need them.
   For more information on codecs, take a look at the following Wikipedia entry:
      - Wikipedia: Codecs
        [http://en.wikipedia.org/wiki/Codec]

  There are applications available which will analyze a media file and
tell you which codecs it requires and whether these are installed on
your system or not. The most popular of these is G-Spot. Simply open
the troublesome avi or mpg file with this app and it will give you the
information you seek. You can download this application from:
     - G-Spot v2.6
       [http://www.headbands.com/gspot/v26x/index.html]

  As for the problem of obtaining the codecs you need, the simplest
solution is to install one of the many available codec packs on your
system. These codec packs contain most of the common (and even
uncommon!) audio and video codecs you might run into. One of the most
popular codec packs is the K-Lite Mega Codec Pack (latest v1.53),
which I would recommend. This will install codecs as well as some
useful tools (such as G-Spot) on your system. You can download the
latest version of this codec pack from:
     - Final Builds Site: K-Lite Mega Codec Pack v1.53
       [http://home.hccnet.nl/h.edskes/finalbuilds.htm#klmcodec]

Hope this helps! If you need any clarifications, just ask!

Regards,
Theta-ga
:)

Well, well, well.  That was one of the most useful answers I've ever
received on this site.!  Gracias.