Larry Li wrote:CPU is not getting near 100%, that's why I assume the CPU is not the bottleneck at my setup.
let me try transcoding the h264 footage and render again, see if there is any performance gain.
Sure. I'm just not sure that means that the RAM is the bottleneck. My personal guess is that it has something to do with the fundamental architecture of DR.
UHD h.264 on the timeline plays back jerky on my systems while using about 38% of the CPU.
Playing an empty UHD timeline in DR takes about 10% of the CPU?!?
Meanwhile, Media Player classic will play UHD h.264 full frame on a 1080 monitor and use 15% of the CPU power while PotPlayer will use only 10% while also playing the video perfectly smoothly.
It takes DR almost 2 minutes to transcode one minute of UHD h.264 to DNxHR HQ
But if you feed it a ProRes stream of the same video, it only encodes about 15 seconds faster.
So no matter how you look at it, the actual load to decode h.264 simply isn't all that much. So I figure that the problems with h.264 and DR probably comes down to an architectural issue with how video frames are served to the timeline (and how well these things are multi-threaded) and that this probably stems from DR's heritage not as an editor, but as a color grading system.
As much as I like the idea of using DR's internal Optimized Media option for its convenience, I've concluded that with UHD, things actually work smoother by encoding externally to DNxHR using Convert V4. It is marginally faster on the encode, and the clips generated play smoother on the DR timeline and put less load on the system.