I'm trying to build ffmpeg from source so I can add libx264 support, but sudo apt-get build-dep ffmpeg gives me:

Reading package lists... Done

Building dependency tree       

Reading state information... Done

Picking 'libav' as source package instead of 'ffmpeg'

The following packages have unmet dependencies:

 libjack-dev : Depends: libjack0 (= 1:0.121.0+svn4538-3ubuntu1) but it is not going to be installed

E: Build-dependencies for ffmpeg could not be satisfied.