Premiere Pro CC not using previews on export

Question

I'm using PP CC on a decked out iMac(i7, 32Gb RAM, 14TB RAID, internal SSD) and my exports are very slow even when "use previews" is checked. Thing is, I don't think PP is using those previews. During the export I can see that aerendercore and importerREDserver are running. The sequence is already rendered so it shouldn't be pulling in the raw files from the red server or going to AE to render the linked ae comps. Right?

Answer 1

I've been through this discussion before ... talk about deja vu all over again! 
The best explanation I have received was at NAB, with two of the heavy-lifter behind-the-scenes staff of Adobe's video programs. Long and involved discussion, one of those where for about the next ten minutes I felt very enlightened on video processing, codecs, and computer hardware design & usage. And then reverted to a normal human status over the next hour. Ah well.
Basically, there's only a couple 'codecs' where it is even possible to utilize previews in a render-out full export. They're huge puppies and most of us don't have the massive-capable machines that can handle that stuff on the fly for editing purposes. As to the rest ... remember, PrPro is like Lightroom, NOT Photoshop. It never makes a complete new 'file' when 'saved' like say Photoshop does, but only stores the info of the changes you have called for to be applied to the original footage, similar to Lightroom. And note, just as Lightroom can create p-views of various sizes up to 1-1, it never utilizes those highly-compressed p-views when you want to create or "export" a final form of the image for use. It takes the recipe of what you've ordered done to the original image and creates a version of that image with that look in the size and file-format (think codec) of your choosing. Which has nothing to do with the file-format (codec) of the internal-use p-view, even a 1-1 p-view.
When viewing a monitor during PrPro, Sg, & AeFx, that's what you're seeing: the original footage with your changes added to it on the fly ... for the most part. In all three programs there are things complex enough that it will create new viewable bits & pieces but in very few situations will it ever completely create a new run of footage. You'd howl if it did ... think of the massive increase of stuff on your drives if it behaved that way! The bits it stores as "Previews" are neither complete new forms of your original footage nor are they of the quality you'd want or the particular nature of pixel-structure for any specific codec you want an output prepared into.
When you render sections, or even entire clips/sequences for previews it renders those frames and sections of frames that are problematic into an internally-chosen codec that is quick for it to use on the fly and looks ok, and constantly intermixes those bits with original frame and the 'recipe' of what is being called for. It does NOT make an entirely new & complete form of the original footage with all changes applied.
Apparently, there has been discussion internally as to whether the "Use previews for export" button should simply disappear unless you are using one of about two video formats that actually "live" in PrPro as full-res/size files. I asked why this hadn't been done, and the response was ... it's been considered. It would save a lot of hassle, grief, and arguments if they did, is what I'm thinking. The vast majority of us don't have one of those rigs that's like four super-Macs built into one "single" computer. Or a mobo with 8 different quad-or-better core cpu's, that sort of thing. We're not working directly in the formats that need such hardware.
Neil