Dropping frames for HD in Kodi on a NUC

[MicWit]

I have just upgraded from my old NUC to an i5 7th gen one. When I try play HD tv recordings on it, it runs chunky, looks like its dropping a lot of frames (the audio is fine). The NUC is both the backend for recording and a Kodi front end for playing. I tried Kodi on another computer and watched the same files over the network without any issues, so it's not the back end causing the problems. I also tried a 4K (96fps) mp4 I downloaded as a sample, and it plays fine in Kodi (in 4K, I think at 60fps). I turned the logger on in Kodi, and in both of them they seem to sit at about 30fps. I'm wondering if it's something in the intel graphics drivers in Ubuntu that has specific problems with the format that mythtv uses?