Andrew: I have the same setup as you (as you know) and now same/similar problem. I used to have a big problem with video playback on 5.5 and 5.1. But thanks to you it was solved.
Now video and audio playback works smooth with N5.1.
But with N5.5 I have clean audio PB until I open video screen (F8). Audio starts to jump and soon audio PB stops. No audio output and no metering on audiotracks.
After reseting VST audio system audio is back, stuttering again and then audio/metering disappears. It seems that audio PB tries to sync to video but fails resulting no audio PB what so ever…
Without audio, video runs smooth on N5.5?! Add only one audio track and insert audio to that track → first stuttering , then no audio. Video PB still smooth…
I can use N5.1 for movie work but this is not good…
So I agree with Andrew, something is screwed in Nuendo 5.5 video playback. It might be system related as it happens on two similar systems, but it is only with N5.5. 5.1 works fine. What was changed from 5.1.–> to 5.5. concerning video engine? And can it be fixed???
Bye / Tumppi