can someone explain to me something

[Senectus .]

How is it that I need to have three media players?

I received a movie from a friend the other day, With VLC I can hear
the sound, with Totem I can see the thumbnail picture but not play the
movie or hear the sound, but with mplayer I can play the movie and
hear the sounds.

It's never the same but.
Sometimes (mostly) it's VLC that will  play the movie fine, other
times it's Totem... surely they're all using the same codecs as each
other.
Why is it that sometimes one can play it but others can't?

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Ubuntu Breezy 5.10
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