[Caesium]

It is jerky only with Advanced deinterlacing. Switch to "Bob". RAM overclocking can also help.

Yep, that does indeed fix it - Bob deinterlacing is fine. Is this a known/accepted limitation in that case? Is Advanced deinterlacing just simply too much for the Pi to handle while also doing subtitles?

I'm not sure I can tell the difference between the two modes, certainly not on that sample anyway. Maybe I'll just make do with Bob