Make only a specific region of a video blurry I have a lower third that  I want to use in adobe premiere. It's slightly transparent and I put an adjustment layer on top to add a bit of blur. When I add some footage to the after effects composition it looks correctly blurred. The problem is when I export it that blur doesn't apply to the footage in Premiere (not even when I import it using dynamic link). Is there a way to make the blur apply to the footage without having to import the entire edited project from Premiere into After Effects? I don't use AE much and I'd hate to keep paying for it only for that one thing.
In your Premiere timeline put two copies of the lower third above each other on top of the footage. Right click on the lower copy and choose Adjustment Layer from the context menu. Now it acts as a mask for any filters you apply to it, affecting only the opaque areas. Apply a blur effect to this adjustment layer and the footage below will blur where the lower third is opaque.



Now because adjustment layers use the opacity of the clip to set the strength of the effect you might find the blur won't be very strong where the lower third is semi opaque (this is what it looks like with the top layer turned off):



You can fix this by making a duplicate of your lower third in After Effects with a more opaque background, and using that as your adjustment layer:



And Voila! Your beautiful lower third with bg blur: