Was looking for answer on this to. I wish Adobe would add in, but will most likely take a long time to implement. I’m posting 4 years later from original. =^D
Thought of this approach and tested quickly. Works! But may not be as easy as black/white painting on linked mask.
CONS: May not be 100%…pending on complexity of what you’re trying to create. For me…doing a hand animation in PS Blank Video Layer in Timeline mode. Be mindful of setup too. A bit tricky to comprehend WHY to do in this order.
Step 1: Create Blank Video Layer — Name is “Art”
Step 2: Create Animation on “Art” video layer
Step 3: DUPLICATE (Ctrl+J) on “Art” video layer — Rename to “Ani_Clip_Mask” — Now move below the “Art” Video Layer.
**NOTE: It’s worth explaining why to duplicate after the animation is created. You must understand how clipping masks work. Please do some exploration. Basically the Layer on the bottom will become the CLIPPING MASK, and whatever pixel/vector art data is present will reveal the layer linked above it.
Step 4: Create a Clipping Mask. To LINK a layer to be CLIPPED by the layer below it: Right click top layer > Create Clipping Mask
**NOTE: I prefer much easier shortcut: Press & Hold the ALT key. Now hover mouse between the 2 layers you want to create clipping mask between…you’ll see an icon appear with downward arrow and square — LEFT CLICK to assign. (You can LEFT CLICK again while holding ALT to unlink clipping mask).
Step 5: Use Erase tool on “Ani_Clip_Mask” layer on desired frames thus MASKING the “Art” Video Layer.
FINAL THOUGHT:
Hopefully, you understand why to duplicate artwork after animated. Otherwise, it’s much more work to get desired result. This is my present work-around until Adobe decides to add in Animated Layer Masks into the Timeline.
(Hope this helps others…I’ve gotten so much help over years on here)