EricLalicata wrote:...fully render cached timeline with a lot of noise reduction etc pre-cached for playback...We insert edit a new logo at the top of the timeline and the entire timeline cache turns red. Why?..Isn't the cache tied to the clip? Why would moving the location of the clip on the timeline make the cache disappear? Shouldn't Resolve know to keep the render cache tied to the clip based on it's source frame timecode? If not, can it be changed to do this?...
There are three categories of cache: Source Cache (now called Fusion Output Cache), Node Cache and Sequence Cache. They each can be invalidated without affecting the others. The goal is enable you to adjust an edit without affecting the cached grade, and vice versa.
Unfortunately the red/blue render bars are not specific to which category of cache is valid. IOW you can do an action that invalidates sequence cache that might have a limited performance impact and the render bar turns red. Or you could do an action that invalidates node cache on a clip with noise reduction, which has a great performance impact yet the render bar turns the same red color. The UI unfortunately does not distinguish which type of cache is valid or not. However you can often deduce this by the time required to re-render. If slow, it is more likely node cache for a compute-intensive effect. If fast, it is maybe sequence cache.
I set up a timeline and put some titles and various effects on it including temporal/spatial noise reduction plus burn-in timecode. If I inserted a .jpg at the start of the timeline, certain portions of the timeline would briefly show red render bars. However that was apparently just rebuilding sequence cache, not node cache.
On my timeline it only did that for regions of the timeline containing multiple layers and only for certain types of effects. For what it's worth, on page 182 the Resolve 18 manual says: "Sequence Cache is a separate cache for effects that are specifically applied within the Timeline in the Edit page. These include transitions, opacity adjustments, and composite mode superimpositions."