OK - firstly, apologies to gda, DocViper and Mini73 for wasting your time on the yavdr-0.5.0-beta!! My fault.
I have now reinstalled yavdr-0.5 and only have the video stutter problem, as originally posted.
As per the attached syslog, every 5 seconds I'm getting some sort of sync/buffer problem which I gather is causing the video to "catch up" and pixelate.
Apr 19 10:11:00 ubuntu vdr: video: audio/video difference too big
Apr 19 10:11:00 ubuntu vdr: video: decoder buffer empty, duping frame (149348/1660) 0 v-buf
Apr 19 10:11:00 ubuntu vdr: video: 16:10:17.870+8888 7839 507/\ms 0+5 v-buf