Aspect Ratios & Resolutions

[Jamaine]

I'm trying to understand, why is it if I have a 1920x1080 file and I convert it for SD broadcast to Mpeg 2 (720 x 480) with a 4:3 aspect ratio, it is letter boxed. But if I try to export that same footage SD broadcast to Mpeg 2 (720 x 480) with a 16:9 aspect ratio it is either window boxed or pillar boxed.

I'm bit confused because they say that all Hd formats are shot in a 16x9 aspect ratio.

The Second question I also have is if you broadcast one of the HD formats in HD on a High Def TV, will it be fullscreen or Widescreen.

 

[edinc90]

Part of it has to do with pixel aspect ratio. That is, the shape of the pixels. Hint: they aren't always squares. Instead of saying 16x9 or 4x3, let's talk about the ratio as a decimal.

An actual square is 1.0. HDTV is 1.33 PAR (pixel aspect ratio.) SD "square" is 0.9, "widescreen" is 1.21.

So, if you convert your HDTV signal to SD widescreen, you can letterbox it and get away with the slight variation in PAR. If you have an SD program that looks squished, it is because the 1.21 source is being squeezed into a 0.9 aspect. This is also called "anamorphic" in terms of SD. There are also anamorphic lenses, but that squished the light onto the sensor, instead of the pixels onto the screen.

It's possible that not all edit programs handle the aspect conversion the same. There are two proper ways to deliver HD original content to SD broadcasters. Either "pan and scan" where you lose the wings and deliver a full screen image, or a letterboxed version where you deliver a full-frame image with black bars. The drawback to the latter is that if the person is watching a letterboxed video from an SD source on a widescreen display, they end up with window framing (black border all around, a combination of letterbox and pillar box.) The display adds the pillar boxes to the already letterboxed content.

If you broadcast HDTV content in HD to an HDTV, the screen will be filled with your entire frame.