Addresses comments in review https://github.com/ebu/ebu-tt-live-toolkit/pull/422#pullrequestreview-35398639
Addresses comments in review https://github.com/ebu/ebu-tt-live-toolkit/pull/422#pullrequestreview-35398639

bbc/ebu-tt-live-toolkit,ebu/ebu-tt-live-toolkit,ebu/ebu-tt-live-toolkit,bbc/ebu-tt-live-toolkit,bbc/ebu-tt-live-toolkit,ebu/ebu-tt-live-toolkit