CURVATURE is now working. The problem was due to the replacement of ´´´IN.video_size / IN.texture_size´´´ (a small number representing the scale between the two sizes) with ´´´global.SourceSize.xy ´´´ (much bigger than the previous number).
SHARPER was made to work too.
@hizzlekizzle: I deleted your vec2 angle variable, which was hardcoded to (0, 0) while I was trying to fix the curvature stuff. Feel free to revert that.
Changed the formatting, tab size is 4 spaces.
Based on the discussion in IRC, I carefully deleted every instance of global.SourceSize.zw, because z = 1/x and w = 1/y and zw is NOT the same as IN.video_size.