Arnavion
commented
6 years ago As the documentation says
After the renderer fires its ready event, libjass.renderers.WebRenderer.resize must be called to initialize its size before starting the clock.
However videojs-ass is starting the clock before calling resize, thus WebRenderer.preRender is getting called before its scaleX and scaleY properties have been initialized. videojs-ass needs to fix this.
(Edit: videojs -> videojs-ass)
Sample set
This happens with a simple implementation of videojs-contrib-ads (heisenbug.html) and with videojs-vast-vpaid (heisenbug2.html), though the latter case is much, much rarer.
I noticed that when this happens, the style of span elements for subtitle lines are missing the font attribute. It seems that something about how both plugins set up ad playback interferes with span styling somehow, even though only one of them makes use of videojs-contrib-ads/
I'm not sure how to trace this further, but because it involves span styling, it seems this is a libjass issue.