Why can't I enable motion blur on certain pre-comps in After Effects?

[TheBigDyl]

I'm working on a fairly simple After Effects project where I can enable motion blur for most layers, but I can't turn it on for two pre-comps and I'm not sure why. In the timeline there is a dash icon instead of the motion blur icon, and it doesn't change when I click on it.

The pre-comps contain only a few shape layers and the only effects applied are some fills. Why can't I enable motion blur?

[Mrtn Ritter · Accepted solution]

This behavior is connected to continuous rasterization setting (CR - the little sun icon).

When CR is turned on for a precomp, this precomp usesed the MB settings of the layers within the precomp, instead of having an own MB setting. I cannot 100% tell you why it's like that, but CR reads in the layer data on each frame and somehow precomp MB settings are dropped in this workflow.

You have precomps with shape layers, which are CR'd by default and so is the precomp. In order to get MB to work, turn of CR on the precomps, or turn on MB on the layers inside the precomps.

I wrote a script a long time ago to handle MB and CR recursivly for all layers in all comps:

https://github.com/mrtnRitter/OptAllLayers

It should still work...

*Martin

[TheBigDyl]

Thank you! Turning on motion blur for the layers within the precomp did it.