The HD movie frame aspect ratio is dependent upon the source format.
For the record, every single reference to 2.35:1 is incorrect. This aspect ratio was used in the 1950's with CinemaScope, a now defunct format. There isn't a single film shot in CinemaScope these days.
So here's how it works....
1.37:1 - 35mm full aperture.
1.33:1 (4:3) - Standard definition television
1.66:1 - not contemporary, used in some Kubrick films e.g. Barry Lyndon, Full Metal Jacket
1.78:1 (16:9) - HDTV frame aspect ratio
1.85:1 - Super 35mm, soft- or hard-matted from 1.37:1.
2.40:1 - Panavision. Mistakenly called "Scope" and 2.35:1. Filmed on 1.37:1 frame using an anamorphic lens.
Every one of these aspect ratios other than 16: will have matte lines when viewed on an HDTV.