Retime Process: Optical Flow is slowing down render times.

For the life of me I couldn't figure out why some of my newer projects were rendering at 20-24 FPS when previous projects would average above 100 FPS. I thought it was the codecs or the files that were submitted to me, or the version of Resolve, I was jumping between different versions of 16 before installing 17.

It turns out that it was the project settings, namely the Retime Process (Frame Interpolation). The older projects were set to Nearest, whereas my recent projects had the template set to Optical Flow.

Not sure if this is a bug but when I have it set to Optical Flow, render times are basically set to the frame rate of the project (24FPS). If I change the setting to nearest, it fully utilizes the CPU.

Any idea why this is the case or is this a common issue?

PC Specs:

Ryzen 9 3900X / Radeon VII / WD Black 750 / 32 GB RAM

Optical flow based retime is very processing intensive. Nearest frame just grabs, as name suggests, nearest frame, so has no impact whatsoever.

And if you want to see something really slow, but in most cases excellent, try SpeedWarp

Optical flow based retime is very processing intensive. Nearest frame just grabs, as name suggests, nearest frame, so has no impact whatsoever.

Is there a way to get it to render faster if I ever need to use Optical flow? Would using the render cache or optimized media speed things up?

Optical flow based retime is very processing intensive. Nearest frame just grabs, as name suggests, nearest frame, so has no impact whatsoever.

Is there a way to get it to render faster if I ever need to use Optical flow? Would using the render cache or optimized media speed things up?

progressively render to a good cache while you're working and then "render form cahe"

or

right click to the clip you need to do Oflow, [render in place] it will create new media and from that point on you're good. (v17 only)

progressively render to a good cache while you're working and then "render form cahe"

Be very careful when using cached renders with retimed clips, and you are using a "roundtrip" rendering workflow (at least to Premiere). If you enable use render-cache for your roundtrip renders, those clips will be rendered with incorrectly retimed frames baked into the roundtrip renders (in a roundtrip workflow, retimes should not be baked into the renders at all!)

progressively render to a good cache while you're working and then "render form cahe"

Be very careful when using cached renders with retimed clips, and you are using a "roundtrip" rendering workflow (at least to Premiere). If you enable use render-cache for your roundtrip renders, those clips will be rendered with incorrectly repeated (or dropped) frames

See: viewtopic.php?f=21&t=130139

Apologies: i don’t do round-trips so I’m not aware of this issue.