jquery media not show player
The two locations specified for sites/default/files are different in your example:

First part: http://demo.dolphin-sch.ir/nagara/fa/sites/default/files/mediaplayer/player.swf?file=

Second part:  http://demo.dolphin-sch.ir/nagara/sites/default/files/audio/12.mp3

I'd check your paths are set correctly everywhere.

EDIT:

This link works fine:

http://demo.dolphin-sch.ir/nagara/sites/default/files/mediaplayer/player.swf?file=http://demo.dolphin-sch.ir/nagara/sites/default/files/audio/12.mp3