Videos not displayed in Ubuntu

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http://askubuntu.com – I have installed Ubuntu 12.04 on my Lenovo machine, having 1.5 GB of RAM and a wide screeen LCD Dell monitor (I think videos have a 16:9 aspect ratio). The problem is I am not able to see videos in VLC or Totem movie players. I'm able to listen to sound, but videos are not displayed. SMPlayer is working well to display video. Could anyone please explain to me how to play videos in other media player? (HowTos)