The whole "sound in silent profile" has a somewhat 'hackish' past, as it was not properly thought of. Some applications just identify themselves as "FMRadio" to have sound in silent profile, fooling Maemo (works only in GTK apps afaik).

The QMediaplayer function from Qt still seems to work fine, but this never ported to PySide on Maemo 5 (it is ported to the Harmattan version). And I guess mafw is still doing fine in CSSU in silent mode

Interesting question is how mplayer implemented it. Version 1.0svn20091221-2 has changelog "* added patch for allowing playing in silent mode". I was not able to find the exact code used for that for now.