how i play movies in this format 720p XviD ?

The movies you want to play that are in the 720p XviD format are designed to only be played on mobile devices, at this point. You would have to be using an iOS device or Android device, and have the appropriate mobile device player that was compatible with XviD. So you cannot watch it on your Mac at this time.

The Xvid component for QuickTime allows users to play & encode Xvids in QuickTime Player. Xvid is a video codec library following the MPEG-4 standard.

https://www.apple.com/quicktime/resources/components.html

http://perian.org/

http://www.videolan.org/vlc/download-macosx.html

https://code.google.com/p/niceplayer/

Thanks ds store for correcting my mis-information. 🙂