I also can not believe nobody has a solution to this issue. We are having a hell of a time working around this because every extra conversion we have to do gives us another generation loss. We’re working on mac, and so far the workaround has been to convert to and work in PRORES 4444 and then export out of AE at DNxHD. So basically introducing 2 generations of loss into our footage.
What is absolutely baffling to us though is that on a couple of our machines with Lion, the DNxHD codec does not work at all in QT 7. But, it works just fine in QT X and AE. In fact, the black artifacting is gone in AE. The problem comes when we try to export DNxHD. All we get is pink and green noise.
I’ve been searching everywhere for a solution to this. There doesn’t seem to be one at this point. If we solve it, I will definitely post here again.
Good luck!