Toshi.des wrote:Hey guys, I am a bit confused with this demonstration of aspect ratios shown in Premiere.
My current understanding is for whatever measurement a 4:3 vs a 16:9 aspect ratio they can have the same pixel area but should have different measurement lengths.
Example: if 720x480 is 4:3 then a 16:9 clip with the same area of pixel should have a longer width and shorter height than 720x480 right?
Premiere's Presets for film though in NTSC shows that they both have the same frame size which doesn't make sense to me.
Firstly, 720x480 isn't
actually 4:3 - 640x480 is. The only reason 720x480 is 4:3 is because of the non-square pixels on a TV. If you divide 4/3, you end up with 1.33 repeating. If you divide 640/480, you get the same result. That only works when you assume the pixels are square, though, as you would on a PC monitor.
TV pixels are differently shaped, based on whether you live in NTSC or PAL land. NTSC's pixel ratio is 0.9, which makes it slightly more wide than tall. Divide 640 by 0.9 and you wind up with ~712 pixels. Then four pixels are padded onto either side and voila, 720x480 = 4:3 on a TV set. This is why MPEG-2 and other types of distro formats have aspect ratio flags to compensate for these PAR differences. A flag signifies that it displays as 4:3, or it can specify a ratio of 16:9, which is called anamorphic flagging. MPEG-2 itself also supports a flag for 2.21:1, but the DVD standard doesn't include support that ratio, nor do any movies I've come across use it either.
The same concept applies to 16:9. 16/9 = 1.78 (7 repeating), if you divide 848/480, you get close enough to that for it not to matter (since 848 is a mod16 res; properly, it's supposed to be something like 853.3 repeatingx480). Likewise, if you take 853.3 repeating and divide it by the 1.2121 PAR that Premiere's window is telling you the Widescreen profiles use, you get ~704 pixels, and you'd treat it similarly - pad the extra distance to 720, 8 pixels on each side (although in practice you tend not to see borders that huge, or only on occasion; older releases are somewhat more prone to it in my experience).
To be far more concise than the above, it's treating your footage anamorphically. DVDs often use anamorphic techniques for storing 16:9, so that the encoding process is optimized (
the guides have an entire section on this).
This is also why I agree with Kionon; it's much easier to deal with this stuff if you just resize to a proper Square ratio (640x480 for 4:3 or 848x480 for 16:9) and use Custom to make the project adhere to those resolutions instead of using one of the templates - leave any AR adjustment stuff for distro and DVD authoring if you feel the urge.