Aspect ratio?

[Dennis98]

@chip75: I think you are misunderstanding sth. I also see aspect ratio for the same thing, as you described in your last sentence.
I don't know the movie or disc, but what I understand from the OP, is sth. like this:

The whole image, the video encode, is 1920x1080, which is an AR of 16:9 (1.78:1). The actual image containing information, without the encoded pillarbox in this case, is 1436x1080, which is the 4:3 (1.33:1) AR.
As the latter is what is interesting, as probably all or at least the majority of BDs have a full frame 16:9 video encode, the AR to enter in the entry would be 1.33:1.

EDIT: Ah, it's a DVD with a 4:3 encode (is that a thing on DVDs?). You indeed mean "16:9 letterboxed to 1.33:1". Then aspect ratio would be 1.78:1. Well, hopefully the explanation helped a bit at least. Always remove letterboxing (black bars horizontally), pillarboxing (black bars vertically) or even windowboxing (black bars all around) for the aspect ratio information.