If you have downloaded videos from websites like YouTube, chances are that it is of FLV (Flash video) format. FLV format is the preferred format for content distribution online. Windows Media Player does not play .flv files. However, by using a plugin called Play FLV, we can play .flv files
Double-click the Play FLV setup file to begin the installation process.
Just click Next till the last step.
Play FLV installer will ask you for permission to download (internet connection required) and install FFDshow which is required to play Flash 7 video files. Click Yes.
Once it is downloaded, click OK to start installation procession of FFDshow.
Click Next a few times to complete the FFDshow installation.
After the installation is finished, double click an .flv video file to open it in Windows Media Player.