error: /opt/local/include/X11/extensions/render.h is being used by the active render port.

[Jean-Michel Pouré]

sudo port -v install ffmpeg-devel
--->  Activating xorg-renderproto @0.9.3_0
Error: Target org.macports.activate returned: Image
error: /opt/local/include/X11/extensions/render.h is being used by the
active render port.  Please deactivate this port first, or use the -f
flag to force the activation.
Warning: the following items did not execute (for xorg-renderproto):
org.macports.activate
Error: The following dependencies failed to build: libsdl xorg-libXrandr
xorg-renderproto
Error: Status 1 encountered during processing.

df -lh
Filesystem     Size   Used  Avail Capacity  Mounted on
/dev/disk0s2   233G   193G    39G    83%    /
/dev/disk1s1   501M   501M   640K   100%    /Volumes/NO NAME
/dev/disk2s2    60M    55M   4.8M    92%    /Volumes/iSkysoft Video
Converter

Pardon my ignorance, but what should I do to build ffmpeg-devel? I am
completely new to MacPorts and thank you in advance.

Kind regards,
Jean-Michel