In Most cases ubuntu is brilliant and at the same time the engineers while making it skipped multimedia applications from prime zone. This is the reason for the popularity of VLC in Linux .
But even if we installed VLC in ubuntu it ll not turn in to default video application. To do same so the following steps
1. Install VLC in ubuntu
for this go to Ubuntu Software center , Search for vlc and install, Waiti for the install to finish
2. Once installation is over goto dashboard, search for details
3.Click on Details , on the resulting window ( see picture) , select VLC player from Video option
done, Now videos will open from VLC player