Two more issues I neglected to fix:
First off the multiplier calculations are wrong since they are based off a default font size of 10px which is not actually what we use. We use a percentage of the video size as specified in CaptionUserPreferences.
The second issue is that for center aligned text, the cue box is offset from center after adjusting the width.
This is because when we specify center alignment, what happens is that we actually calculate the left/top css value such that the cue looks centered.
Thus we also need to adjust the left/top property value (by the difference in width / 2) if we're not centered such that the box remained in the center.
Created attachment 236413 [details]
Comment on attachment 236413 [details]
View in context: https://bugs.webkit.org/attachment.cgi?id=236413&action=review
r=me, but please address the possible zero-base-font-size issue I mentioned.
> + double authorFontSize = videoSize.height() * cue->baseFontSizeRelativeToVideoHeight() / 100.0;
Can baseFontSizeRelativeToVideoHeight ever be zero (I think it can be)? If the author could arbitrarily set this to zero, I think we should check and fall back to that minimum (10 pt) value from the CSS.
committed with review commented applied: