I have scrapped a project here and there, because this unwanted and erratic Render Preview made it too annoying and cumbersome to continue. One spends less time editing and more time waiting for separate portions of the timeline to render a preview. Then later, some of these renders disappear, and then later PD9 re-renders the exact same ones it removed. And all the while, I never clicked or asked for rendered preview in the first place.
Then I start over from scratch, re-creating the project “exactly” the same way, and this time no unwanted auto initiated Render Preview occurs throughout the whole project.
So it has not been my experience that altering one’s preferred timeline arrangement (e.g. Clips, images, transitions, etc), makes much of a difference with respect to a Render Preview starting up by itself.
There's something that is in some cases is causing PD9 to trigger a preview render, and I believe it’s possibly owing to one having a lower to midrange computer, or a less than a 1gig graphics card perhaps(?). But if you do have a high spec'd rig aney89_16, with a powerful card, then my theory is wrong I guess.
Still, the Render Preview is an “option”, and optional features/tools should never engage themselves on their own, regardless of what’s in the timeline. Even in cases where it may indeed be advantageous to render the preview (to lessen the load on one's rig), it should still be the user’s choice to either initiate this “option”, or decide to just live with the occasional hangs and stalls in the preview when creating a project.
Just my 2 cents worth.
-CP-
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