The codec or more properly the container that is hosting the content *.mp4 could be a variety of formats the extension.
whatever filename.mp4 is just the container. Any mp4 file will play in any player provided you have the right decompression codecs installed on the pc you want to play the file on.
If you don't want to install a codec pack like k-lite mega codec pack on your pc to be able to play the file in windows media player or whatever your default player is, or maybe this is all jubberish to you.
Then get vlc media player it has the codecs built in to play pretty much everything. You can get that here
http://www.videolan.org/mirror-geo.p....9.4-win32.exe
It is lightweight and will not take over as your default player unless you leave the boxxes checked under video and audio near the end of the install. After its installed just open it up and browse to the file, or drag the video to the vlc icon for vlc to open it up.
This still won't help the person you are e-mailing the files 2 unless they have the proper codecs installed on their pc as well. To make it easy on them you are going to have to convert it into a basic file format like *.avi or *.wmv wmv is your best bet as 99% of pc's come with windows media player already installed.
There is a simple free to use program that will convert the file to wmv or avi for you it is called media coder. You can get that here
http://mediacoder.sourceforge.net/mi...0.6.1.4196.exe
Thier site contains all the help or info you need should you encounter problems.
http://mediacoder.sourceforge.net/index.htm