Set Mplayer as default movie player in ubuntu

I have several movie player in my ubuntu include Mplayer,Realplayer,gstreamer (the default movie player).Everytime I click on a vedio file,gstreamer starts up with an error on codecs.So I delete gstreamer by following command in terminal(It cannot be erased from Application–>Add/Remove…)

sudo apt-get autoremove totem-gstreamer

I want to use Mplayer as my default movie player,but other movie player starts up when I click video files.And following is what I did with it.
Right click on a video file,select Properties and navigate to Open With tab,tick Mplayer.If it’s a .mp4 file,next time you open a .mp4 file,Mplayer starts up.If you remove all other applications in the box only Mplayer left,all video files starts up by mplayer for default.

To set default player for firefox

Type about:config in address bar,click on “I promise,I’ll be careful” when prompt.Search “network.protocol-handler.app.rtsp”in Filter and change it’s value to “mplayer”.If it’s not exist,right click on blank and select  New->String

to create.Enter “network.protocol-handler.app.rtsp”,”mplayer” in turn.

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