If you have a SBS (side by side)/polarized/3d video, and you want to get the 3d effect without owning a 3d monitory (capable of producing polarized light), you can do so with the classic red-blue anaglyph 3d glasses; but first you have to convert the video to red/blue 3d format. You can use ffmpeg to do so.
ffmpeg has the capability to use mplayer/mencoder filter with -
ffmpeg -vf mp=[the mplayer filter]
The stereo3d filter of mplayer does the trick here, it converts sbs to anaglyph 3d, and I have to say conversion is good!
ffmpeg -i sbs.mp4 -vf mp=stereo3d -acodec copy -threads 10 -b:v 10000k -preset ultrafast -vcodec libx264 ~/test2.mkv
You can also use mplayer to play the SBS video by converting it to anaglyph in real time using the same video filter -
mplayer -vf stereo3d -vo gl_nosw/gl/gl2
The video driver has to be some form of gl for this to work. If you want to use xv, use the scale filter also -
mplayer -vf stereo3d,scale -vo xv
To get this working in smplayer, in the advanced options > options for mplayer > video filters
to the filter chain.
Also you need to change the video output driver to gl/gl2 etc... if you're not adding the scale filter.
You need the latest mplayer for conversion to be fast. If it still doesn't work, you may try out mplayer2.