I have an .mp4 file which I've converted via Compressor to ProRes 422, maintaining the original frame size (320x240). However, when I import this to FCP, it seems to change to 427x240. I've checked the sequence settings, frame size is at 320x240, the pixel ratio is set to square and I've enabled Anamorphic (16x9). It now seems to have the correct size in the Canvas window, but when I export (I've tried various formats) it comes out as 427x240.
Would anyone be able to advise as to what may be causing this and how to fix it ?