I'm trying to combine a gradient and a blur effect as a mask over a video track.

I can get the mask created via Pan/Crop and apply a Gaussian Blur to that but the blur is constant and I want it to be gradual. What I'm trying to do is create a 'fake miniature' look by mimicing the depth of field of a tilt/shift lens.

Where I'm having difficulty is combining a gradient with the blur effect.

I've duplicated my video track, created the mask via Pan/Crop and applied a blur to that. As noted above, the blur is constant rather than gradual.

I've tried creating a new, empty track above the dupe and dropping a linear b/w gradient onto that, making that track a mask but that doesn't work. Or at least not the way I'm trying to do it. I've tried to create a mask on the gradient layer via Pan/Crop but that doesn't work.

Thanks.