mp4 in RoboFont

[sarahtilley]

DrawBot.roboFontExt/lib/drawBot/context/mp4Context.py", line 45, in _writeDataToFile
  File "/Users/sarahtilley/Library/Application Support/RoboFont/plugins/DrawBot.roboFontExt/lib/drawBot/context/tools/mp4Tools.py", line 23, in generateMP4
  File "/Users/sarahtilley/Library/Application Support/RoboFont/plugins/DrawBot.roboFontExt/lib/drawBot/misc.py", line 317, in executeExternalProcess
RuntimeError: 'ffmpeg' failed with error code 1