2.21:1 is not a valid DVD aspect ratio flag (DVD only allows 4:3 and 16:9 flagging), but all the MPEG-2 encoders I've ever seen have a setting for doing 2.21:1. Which makes me think it's defined as an 'official' ratio in the MPEG-2 spec (and the aspect ratio listing above confirms it was in the MPEG-2 part), but since it's not used very much at all day-to-day, it was left out of the DVD specifications. I mean, to my knowledge, no widescreen TV ever had a 2.21:1 ratio, since (as per that link) it was developed as a film ratio in the 1950s but was still rarely used. Most, if not all, widescreen televisions and monitors are 16:9 or 16:10, although I'd imagine some ultra-widescreen models exist that are 2.39:1 to match the common film ratio.
Case in point, if you try to make HCenc use 2.21:1, it tells you it's not DVD compliant.
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Originally Posted by asarian
(I used 1040, btw, as I think that's what it's actually supposed to be)
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Technically speaking, that's not what it's supposed to be. When speaking in absolute terms, you don't round the result (actual 16:9 at 480p is a width of 853.3 repeating, but it's usually rounded to 848 to account for mod16*, 856 for mod8, 852 for mod4, or 854 for mod2). But encoding programs don't like having non-integer (and in many cases, a non mod-[32|16|8|4|2] number), so it has to be rounded by necessity, and generally, human eyes don't tend to notice the relatively minor distortion that results (1.85 is close enough to 16:9 that in many cases it gets rounded down or cropped when put on DVD). The alternate tactic would be not to divide the width by the ratio, but to multiply the height by it. In which case, you'd get 1998x1080 for 1.85:1, or if you were dead-set on a height of 1040, 1924x1040.
*which also includes mod8, mod4, and mod2, but going 5 pixels down makes less sense when using the others because they can get closer to 853 than mod16 can. With mod16, you can use 848 or 864, and 848 is closer. 1.85:1 at 480p is 888x480, which is compatible with mod8, 4, and 2, but not 16 (which needs 880 or 896).