HD Source to SD Broadcast

Andy_L wrote on 4/18/2012, 9:46 AM
One of my films is now available on-Demand on TV on the Ski Channel. This is an HD source which has been converted to a 4:3 SD picture by letterboxing, and when I watch it on my HD TV, somewhere in the signal chain the picture is being stretched to fit.

I'm pretty sure I've got my TV and DVR set to original format, so maybe the stretching is happening before it even gets to my TV. Regardless, most people are going to watch this "stretched" on a HDTV, and it looks kind of...terrible.

As far as I can tell, this is the reality of US broadcast SD right now: there is no 16:9 standard in use.

But I started thinking, and I realized I could "pre-pinch" my HD footage, so that when it's letterboxed in 4:3 and then stretched, the pixel aspect looks normal.

Question 1 is does anyone know the magic pixel aspect number for converting square pixels which would then look normal when stretched? And Q2 is, is anyone doing this for SD broadcast?

I swear some of the letterboxed SD programs look like they've been corrected so that the aspect ratio is normal, on channels like Oprah's network, for example.

??

Comments

Chienworks wrote on 4/18/2012, 11:12 AM
I think you probably mean "pillarboxing", not "letterboxing".

If you render a widescreen SD version with a PAR of 1.2121 (assuming NTSC) then you'll preserve the full widescreen frame. Unfortunately each individual broadcaster and re-broadcaster can mangle and remangle it in many different ways. For example, i get FOX on two different cable channels and can see the same show being rebroadcast by both side-by-side. I get the SD feed and one might take the 16:9 HD source and show it widescreen SD, letterboxed in 4:3, while the other crops it to 4:3 and shows it pillarboxed, which then gets reduced to fit in a letterboxed 4:3 frame. I end up seeing a tiny picture in the middle of a sea of black border.

Can you deliver HD to the TV station? At least that way any HD viewers will get it unadulterated.
Andy_L wrote on 4/18/2012, 12:31 PM
No, I definitely mean letterboxing. My understanding is that there is no DVD widescreen equivalent format for SD broadcasts in the US. It's always delivered in 4:3 SD.

But it seems like it would make sense to produce a 16:9 anamorphic pinched within the 4:3 spec, because then that would unstretch on a consumer's HD tv and look very close to normal aspect ratio. But is anyone actually doing that?

Andy
Chienworks wrote on 4/18/2012, 2:37 PM
I can tell you for sure that at least someone is doing it. There's a local dirt track car race show that comes on very late night in my area. It occasionally pre-empts the British sit-com i like so i've ended up recording it unknowingly a few times. My signal path is SD analog cable -> tuner -> S-video -> AV-DV converter box -> firewire -> Vidcap -> DV .avi file. When the program starts, the widescreen flag is set and the playback goes from 4:3 to widescreen automatically. Interestingly enough, it won't do this live while recording, but only when playing back what was recorded.

However, by definition, rendering widescreen SD with a PAR of 1.2121 is the "pinched" file that you are looking for. This must be exactly what the car race folks are doing. Of course, if some viewer's TV doesn't stretch it, or they're using an old 4:3 TV, it will look "tall'n'skinny" to them.

And of course, any step along the way can alter or delete the PAR flags, crop the image, stretch it, add pillar/letter bars, or any number of other things.
Andy_L wrote on 4/18/2012, 4:40 PM
Okay, apparently there IS a widescreen broadcast standard, and it's called 16:9 anamorphic. Just like you said, it's the full HD picture pinched into a 4:3 frame, which is then unwrapped at some point in the signal chain before or at your TV (I'm not sure where). Just got confirmation that their distribution company supports it.

Apparently Fox is/was doing this for some sd secondary channels, and others. What's interesting is that not everyone is doing it--flipping through channels today I can find stretched, letterboxed HD material, which always looks terrible. Why anyone would broadcast that signal (in the US, at least) when anamorphic is available is beyond me.

I'm still not sure what the best way to do this with Vegas would be. Maybe nest the project, and then change it's pixel aspect properties to the right ratio (1/1.2121*.9 ?), make sure crop is set to match output format (Standard 4:3 DV), and export.
Chienworks wrote on 4/18/2012, 4:46 PM
How about .... create a widescreen project and render to Widescreen DV ? That way Vegas takes care of all the details for you.
Andy_L wrote on 4/18/2012, 6:02 PM
That would be too easy! :)

I'm not sure whether DV widescreen corresponds exactly to SD 16:9, but it is probably close. More info (and confusion) can be found here:

http://en.wikipedia.org/wiki/Standard-definition_television