I'm sorry I remembered wrong I downloaded it.
I had extra-testing and extra-devel enabled when I did an apt-get install

I got the plugin from here:
http://bundyo.org/maemo/mplayerplugi...50-1_armel.deb
and installed it with dpkg -i mplayerplug-in_3.50-1_armel.deb

I deleted the settings in /home/user/.mplayer/config

I made a new /home/user/.mplayer/mplayerplug-in.conf:

vo=xv
ao=alsa
cachesize=4096
cache-percent=25
noembed=1
framedrop=1
softvol=0
prefer-aspect=0
download=0
keep-download=0
dload-dir=/home/user/MyDocs
qt-speed=high
showtime=0
enable-wmp=1
enable-qt=1
enable-rm=1
enable-gmp=1
enable-dvx=1
enable-mpeg=1
enable-mp3=1
enable-ogg=1
enable-midi=0
enable-pls=1
enable-smil=1
enable-helix=1
nomediacache=0
nopauseonhide=0
rtsp-use-tcp=0
rtsp-use-http=0