Incorrect rendering of CEA608 captions

Created by: squarebracket

Environment

• Link to playable MPD file: http://vm2.dashif.org/dash/vod/testpic_2s/cea608.mpd
• Dash.js version: nightly
• Browser name/version: Firefox, Chrome
• OS name/version: Linux

Observed behaviour

Nightly now incorrectly renders the size of CEA608 captions when using the TTML renderer. For the CEA608 test stream, it renders correctly when at full size. However, opening the console cuts off the bottom of the captions div:

Having the console closed is obviously the normal use case, but I get much bigger problems with real-world captions:

Captions seem to have enough space when viewing the stream in fullscreen:

Do I now need to manually set fontSize or something? Or is this just a bug in determining video size when not fullscreen?