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I wonder if others miss this ability as well: I'd like to be able to select one or more frames, but over lots of layers, and be able to apply an action over all of them. Examples: I have several layers of coloring and want to set the same value for "repeat frames" to all of them. Or erase all of these frames (with or without mask applied). Or set "+1" exposure to them. Or apply transfrom on them.

Currently I can only select a bunch of layers and change frame durations in all of them at once. Am I missing something, or is there a trick to that?

Oh this would be great. (set +1 is already possible with a button from the "handy panel", as far as I know)

Yes, +1 exists, but I'm searching for ways to repair existing scenes, without changing the timeline. Problem at hand: a certain portion animated (and colorized) on 2's needs to be on 1's, so I need to clean every second frame in each layer.

(I found this in other complex software as well: most functions are streamlined for the purpose of creating something, which is all nice if you work according to plan. But for a more chaotic workflow like mine, or for revisions and corrections, things are not so easy. We all know that one client who demands fundamental changes at the end of production ... we try to plan ahead of this, but are not lucky enough all the time.)

Yeah I guess in the current engine it's hard to code but this to me should be standard hope we will see selections across layers one day

For now you can use the scripts in the custom panel to add or remove exposures vertically, and there is some scripts as well in my storyboard tools to modify exposures vertically. Should be scriptable to kind of apply a script vertically on selected layers or selected range, but to have "both" is a bit of a headache. You can lock layers you don't want to me changed, or use layer groups instead of layer selection
I wish we were able to select a timeline range + multiple layers but for now we can't