/etc/cfengine/debian-edu/cf.mplayer is in debian-edu-config 1.702.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 | #
# Configure mplayer to work for more sites
#
editfiles:
  debian.workstation|debian.standalone::
    # Configure mplayer to use TCP for RTSP, instead of UDP.  It has a
    # higher chance of working inside firewalls and NET routers, and
    # seem to work with more RTSP sites.  It should get
    # http://www.filmarkivet.no/open/ working (BTS #491403).
    { /etc/mplayer/mplayer.conf
      AppendIfNoSuchLine "rtsp-use-tcp=1"
    }
 |