Media Player in Windows has been able to play the popular video files like AVI, MP4, MPEG and others. However, some video type such as MKV, FLV (YouTube video), 3GP (from mobile phone) can not be played without a correct codec.
Or you may find MP4 (H.264) video that only play voice but the video does not show up (as well as many file extensions like rmvb, xvid, ogg, FLAC WebM or audio files, ogg, mod, ALAC). To play that video in Windows so we can watch it is by installing a video codec called shark007.
There are also other alternatives to play video file such as K-Lite, but Info Technology prefer shark007 because it is easy to install and configure.
How to play FLV - MKV - RMVB and 3GP video in Windows:
A. Download shark007 from the following link and select the OS: XP / Vista , Windows 7 or Windows 8.
2. Install the application that you just downloaded then open the Settings application from the Start Menu -> shark007 Codecs -> Application Settings
3. Check the box marked "shark007 Suggested Settings" (recommended).

4. You can also change the settings manually codec used for each type of multimedia file. Don't forget to click the tab Help -> Windows Filetype Associations when the setting is done manually.
After you done all of the above steps, then your Windows Media Player will be able to play MKV, FLV, RMVB, 3GP, MP4 video file and other multimedia file extension perfectly. (Note: An additional feature is to display video subtitle (SRT) and also the thumbnail video in Windows Explorer)