[defrost]

There's a few reasons, I suspect fixed resource depth might be factor in poor hardware single pass encoding ...

What does limit them, though, is pseudo real time single pass pipelines.

I see the best encoding results from two pass - one fast run to work out the easy compress and hard compress parts of a video and then a second pass to get the optimal results on a stream that's already got a budget in mind for each section through the advantage of foresight as to what's left to do.