Preroll and Visual Ad Delivery for SCPR.
FFMpeg (2.13+) must be installed with fdkaac and lame.
On OS X, you can use Homebrew:
# lame is installed by default
brew install ffmpeg --with-fdk-aac
On Linux, you'll need to compile manually. See circle.yml for the step-by-step list that gets run on Circle CI to install ffmpeg.