quarter-pixel motion

Quarter-pixel motion compensation, much like half-pixel, is achieved through interpolation.

H.264 decoders always support quarter-pixel motion.

Quarter-pixel motion is derived by linear interpolation of the halfpel values, to save processing power.

The quarter-pixel motion compensation feature of ASP was innovative, and was later also included (in somewhat different forms) in MPEG-4 Part 10 and VC-1.

Quarter-pixel motion (also known as Q-pel motion or Qpel motion) refers to using a quarter of the distance between pixels (or luma sample positions) as the motion vector precision for motion estimation and motion compensation in video compression schemes.