Do I have to keyframe the Vignette Centre property so it stays centred in the frame rather than on the clip?
If the clip is a different size to your frame, and the effect is applied to the clip, then it will center on the clip, and move with the clip if you change the layer's position. In this case, the easiest solution would be to add a grade layer above the clip, and apply the effect to the grade layer. Then you can move the clip however you like, without moving the vignette. You could keyframe the center instead, but its more work for the same end result.
Ok thanks. I'm working in Adobe Premiere Pro so I can't use grade layers but I might be able to apply this in principle.
Yes the clip is larger than the frame - forgot to mention that.
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