> I often get comments saying “[720x480]’s not not a 16:9 resolution” or “that’s not real 480p”, but “480p” encapsulates a range of resolutions and aspect ratios and 720×480 is the resolution the Xbox considers to be 480p (so take it up with Microsoft, not me…).<p>Take it up with some ITU dudes in the 1970s actually: <a href="https://tech.ebu.ch/docs/techreview/trev_304-rec601_wood.pdf" rel="nofollow">https://tech.ebu.ch/docs/techreview/trev_304-rec601_wood.pdf</a><p>“The February 1980 note further suggested that the number of samples per active line period should be greater than 715.5 to accommodate all of the European standards active line periods. While the number of pixels per active line equal to 720 samples per line was not suggested until the next note, (720 is the number found in Rec. 601 and SMPTE 125), 720 is the first value that “works”. 716 is the first number greater than 715.5 that is divisible by 4 (716 = 4 x 179), but does not lend itself to standards conversion between 525-line component and composite colour systems or provide sufficiently small pixel groupings to facilitate special effects. Arguments in support of 720 were provided in additional notes prior to IBC in September 1980.<p>[…]<p>As noted above, Rec. 601 provided 720 samples per active line for the luminance channel and 360 samples for each of the colour-difference signals.<p>When the ITU defined HDTV, they stipulated: ‘the horizontal resolution for HDTV as being twice that of conventional television systems’ described in Rec. 601 and a picture aspect ratio of 16:9. A 16:9 picture ratio requires one-third more pixels than a 4:3 picture ratio. Starting with 720, doubling the resolution to 1440 and adjusting the count for a 16:9 aspect ratio leads to the 1920 sample per active line defined as the basis for HDTV [9].<p>Accommodating the Hollywood and computer communities’ request for ‘square-pixels’, meant that the number of lines should be 1920 x (9/16) = 1080.<p>Progressive scan systems at 1280 pixels per line and 720 lines per frame are also a member of the ‘720-pixel’ family. 720 pixels x 4/3 (resolution improvement) x 4/3 (16:9 aspect ratio adjustment) = 1280. Accommodating the Hollywood and computer communities’ request for ‘square-pixels’, meant that the number of lines should be 1280 x (9/16) = 720.<p>Therefore, most digital television systems, including digital video tape systems and DVD recordings are derived from the 4:2:2 basic standard format. The 720 pixel-per-active-line structure became the basis of a family of structures (the 720-pixel family) that was adopted for MPEG-based systems including both conventional television and HDTV systems.”