I find a way to use mplayer slave mode for previsualisation.
My wm is fvwm-crystal. With it, all that is needed is to change the video player into amule preferences:
fvwm-crystal.mplayer-wrapper file <username> %PARTFILE
where <username> is your login name.
Without fvwm-crystal, you can get fvwm-crystal.mplayer-wrapper from
http://fvwm-crystal.svn.sourceforge.net/viewvc/fvwm-crystal/bin/fvwm-crystal.mplayer-wrapper?revision=7. You must also create the pipe used to communicate with mplayer slave mode:
mkfifo /home/<username>/.mplayer/pipe
and start mplayer with something like:
mplayer -ao jack, -menu -fs -fixed-vo -slave -idle -input file=/home/<username>/.mplayer/pipe
.
"-ao jack," will try JACK for sound output and fall back to the first other sound server like ALSA.
"-menu" will launch the OSD menu, available from fvwm-crystal audio button or from a mplayer key binding.
"-fs" will launch mplayer in fullscreen.
I find the slave mode of mplayer more convenient. It is more robust and you can send command to it. It is documented here
http://www.mplayerhq.hu/DOCS/HTML/en/control.html#slave-mode.