mplayer is started in slave mode by giving it the -slave option.
Your application holds an IO pipe to the mplayer, and you send commands to mplayer's stdin. mplayer returns information on its stdout.

If you know how to read some Python, you could take a look at https://garage.maemo.org/plugins/scm...ox&view=markup

It's basically just sending commands and waiting for an answer from mplayer. Using nonblocking IO avoids that long response times im mplayer block your application.