Anamorphic SD true aspect ratio
While experimenting with effects applied to different aspect ratios I came across an interesting "anomaly".
It turns out that 720 x 480 anamorphic widescreen video has an actual aspect ratio of 1.81818...: 1, even when applied to a 16:9 (1.7777... : 1 a.k.a. 16:9) project. The horizontal edges are obscured by the project size "crop" by ~9.5 pixels on each side (but not removed/cropped).
The resulting width, normally expected to be 853 (.333... but there's not such thing as a fractional pixel) is actually 872 (which is measurable if you know how).
Typically, in SD "broadcast" there are allowances for "overscan". However, I do not understand this particular case, and so far, it seems to be ONLY this case. (Any explanations?) And, there is NO overscan vertically!
To make the video fit precisely into 16:9, this requires a horizontal scaling of 97.8% (give or take a few 100ths... again... fractional pixels). [I arrived at 97.8 first by trial and error, then to get to the math involved, if you divide "should be width" of 853 by the actual width of 872, you get 0.97821101 (times 100 to get to percent), but you don't have to be that precise.]
As an example, I created a "border" effect (applied to the media) which has equal distances from the edges horizontally and vertically. In 480 anamorphic, the result is this:
The top border width is much wider than the left border width.
After applying the 97.8% Scale>X correction
the borders are equal widths again - and *notice* that the image does not sustain the project size "crop" inherent in all other clips with the "Fit" Spatial Conform setting. The media is *there* to be able to fill the space!
I have searched everywhere I know to look and have not found a reasonable explanation for this. Is this an industry wide practice? (stretching/scaling the horizontal aspect for an overscan) or is this just Final Cut?
[Not that it should make any difference anymore...haha...]
If there are no explanations for this behavior, then hopefully, there is some meaningful information here for you if you find yourself ever having to deal with anamorphic widescreen 720x480 media.