Why does webdl has this resolutions?

[android]

I have downloaded many webdl movies from internet
but they are in resolution which never seen before..like i have one movie its resolution is AMZN.WEB-DL.1248x520
Why doesn't its in 1280×720?
Does Amazon's HD resolution is 1248×520 instead of 1280×720?

Some movies webdl has 1920 x 800 resolution

[jagabo]

First of all, it's a 2:4:1 movie so there's no reason for a 16:9 frame size (most theatrical releases are not 16:9). Secondly, as to why it's not 1280x532, maybe it's a matter of wanting to meet a certain bitrate at a certain quality. Thirdly, who cares.

[android]

I have done some research..and found that if movies watched on netflix, amazon etc sites on 16:9 display tv or monitor then it will display in letterbox..mean top and bottom have black bars..am not sure about this because I don't have paid subscriptions but this can be the reason why webdls have 1248×520..they cut top bottom black bars