1: Oh no. After Effects doesn’t let you RAM preview an alpha channel.
My workaround is an adjustment layer with Shift Channels effect with all shifted to alpha. Make it a guide layer so it doesn’t accidentally render.
2: When I change a mask After Effects needs to recache all the frames.
My solution. Leave the layer alone and have masks on a seperate layer.Turn on disc caching so you have somewhere to save the caching.
3: Option click the mask in the composition window to turn on motion blur for it
Submitter: Tristan Summers