[Ian Leo]"Hi. I've been seeing some rotobrush tutorials and videos and found it very useful."
[Ian Leo]"Is there a way to get in in After Effects CS4?"
No. Rotobrush is CS5-only.
If you choose to upgrade, remember that AE CS5 requires 64-bit plugins (CS4 and earlier used 32-bit plugins), so you will need to get updates for all your plugins. Some are paid upgrades, and others are free updates -- check with each developer for specifics.
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