nHD is a display resolution of 640 × 360 pixels, which is exactly one-ninth of a Full HD (1080p) frame and one-quarter of an HD (720p) frame. Pixel doubling (vertically and horizontally) nHD frames will form one 720p frame and pixel tripling nHD frames will form one 1080p frame.
One drawback of this resolution is that the vertical resolution is not an even multiple of 16, which is a common macroblock size for video codecs. Video frames encoded with 16×16 pixel macroblocks would be padded to 640 × 368 and the added pixels would be cropped away at playback. H.264 codecs have this padding and cropping ability built-in as standard. The same is true for qHD and 1080p but the relative amount of padding is more for lower resolutions such as nHD.
To avoid storing the eight lines of padded pixels, some people prefer to encode video at 624 × 352, which only has one stored padded line. When such video streams are either encoded from HD frames or played back on HD displays in full-screen mode (either 720p or 1080p) they are scaled by non-integer scale factors. True nHD frames on the other hand have integer scale factors, for example, Nokia 808 PureView with nHD display.