understanding rendering with "use previews"

[getho]

This is a small thing, but I'm curious:

Sometimes when I render using previews it whips though it in seconds (I have my previews set to cineform 10bit).

With the whole piece rendered (green) it sometimes gets to a clips and appears to have to re-render it.

For instance just rendered out a piece. One clip was 4k with noise reduction and it slowed to a crawl for that, then carried on at top speed.

Just trying to get my head the mechanics of it.

[R Neil Haugen]

Noise reduction ... either audio or video ... is typically re-done at export in my experience.

Neil

[getho]

ah righto! good to know thanks neil

[R Neil Haugen]

It's a frequent complaint ... that "hey, I rendered out my video noise reduction into previews, and it's completely redoing it on export ... !"

I think the assumption on the part of the engineers is that the export ​could​ be to a different codec/frame-size/rate whatever, so ... to be safe, they do that and audio noise reduction on export. If so, I understand it's an attempt to be "safe", but ... it can be annoying with a sequence with a ton of heavy things all pre-rendered and yet ... re-rendered on export.

Neil

[excited_Genie16B8]

Noise reduction ... either audio or video ... is typically re-done at export in my experience.

That's...odd.  With Previews rendered and Use Previews checked, the effects used should be irrelevant.

[SAFEHARBOR11]

Agreeing with Jim. What drive do the previews render to? Maybe storage is not fast enough for the heavy codec and that is slowing things down?

[Kevin-Monahan]

Hi Getho,

Sometimes when I render using previews it whips though it in seconds (I have my previews set to cineform 10bit).

With the whole piece rendered (green) it sometimes gets to a clips and appears to have to re-render it.

For instance just rendered out a piece. One clip was 4k with noise reduction and it slowed to a crawl for that, then carried on at top speed.

Just trying to get my head the mechanics of it.

Sounds like a bug. Which NR plug-in were you using? Do you have this problem with any other effect? Have you tried a different smart rendering codec like ProRes (if on Mac) or DNxHD?

Thanks,
Kevin