[Chris Montel]

Hi everyone, just a complementary message to say that, yes, Mr Ebbert’s advice does work, and for those like me who need more details, it goes basically like this :

You have already two keyframes changing the shape of a mask.

-paste Dan’s expression as formulated above in the mask path field.

The slider control can either be applied to the same layer as the mask path, or on a separate layer (I chose a null) if you have several. Dan’s expression to be applied to the mask path(s) becomes in this second case :

control = thisComp.layer(“Nul 1”).effect(“Slider Control”)(“Curseur”);
t = key(numKeys).time;
mask(“Mask 1”).maskPath.valueAtTime(t*control/100)

Apply the slider control and write the following expression :

loopOut()

in its slider control field. Create three keyframes, one as 0, the second as 100 (both share your two mask path’s keyframes), and the third 0, and you’re good.

(note) for my particular purpose I was able to write 0 and 1 instead of 0 and 100, by deleting the “/100” in Dan’s expression, but maybe that percentage has an advantage I am not aware of !

thanks again, this advice saved me a good deal…