mplayer plug-in not playing some streams

[Novembre]

Hi,

I have installed mplayer-0.99.10_14 and mplayerplug-in-3.45 using packages
on my 7.0-RELEASE machine which runs Firefox 2.0.0.12. I am not able to see
*some* online content, though, and I couldn't find any pattern.
For example, going to http://www.davidgilmour.com/dvd.htm , I can see the
Windows Media streams (both low and high resolution versions), but QuickTime
and Real Player streams are not played at all --- a new tab opens in
Firefox, and I see "Getting playlist..." and "Connecting to server..."
messages, but then it says "Stopped" and that's it!
But, if I go to http://www.satriani.com/podcast/Satchafunkilus/ and click on
any of the podcasts (they are in .m4v which, if I'm not mistaken, is just a
container for QuickTime .mov videos), mplayerplug-in plays them flawlessly.
Another example for QuickTime is
http://www.vai.com/SightsSounds/video_vault/index.html where all the videos
can be played perfectly.
As for Real Player, I see watch BBC Persian website's videos in Windows
Media (e.g. this one about Euro2008 games
http://www.bbc.co.uk/persian/meta/dps/2008/06/bb/080606_op-euro2008_16x9_bb.asx),
but if I choose Real Player as my format, I can only hear the sound
and
no video is played!

I would appreciate any help :)

Thanks a lot