|Okay, I did a search for Track Matte and found a great tutorial for PPro 1.5. Unfortunately, Track Matte workflow has changed a lot since 1.5 (now it works correctly). So...|
Here's the deal: Place indentical clips on tracks 1 and 2 so that they are lined up and in sync with each other. Create a solid block in the titler over the portion of the image you want to blur. Place the title in video track 3 immediately over the clips in V1 and V2. Stretch the title to be the same length as the video clip(s). Apply the Track Matte Key to V2. With the clip in V2 selected, set the Matte to Video 3 in the Effects Controls panel. Now apply a blur to the clip in V2 (default blur level is zero, so you need to crank up the value). This should give you the effect you're looking for.
Note: If you want to have a hard edge on the blurred date, drag the Track Matte effect below the Blur effect in the effects control panel. Hard edge - Track Matte below Blur. Soft edge - Track Matte above Blur.