Start by installing Homebrew and use this to install ffmpeg
:
/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
brew install ffmpeg
Now install the TamperMonkey plugin for your Chrome browser and install the questo script
If you open a video on iplayer you will see a script under the video. Run this using Terminal to download the video.
http://www.renevolution.com/ffmpeg/2013/03/16/how-to-install-ffmpeg-on-mac-os-x.html
https://andrealazzarotto.com/2015/02/20/how-to-download-bbc-iplayer-videos/