Re: Grabbing 4:3 and 16:9

[Michel Bardiaux <mbardiaux@mediaxim.be>]

Daniel Glöckner wrote:
> On Tue, Feb 26, 2008 at 12:19:39PM +0100, Michel Bardiaux wrote:
>> Here in Belgium the broadcasts is sometimes 4:3, sometimes 16:9. 
>> Currently, the card goes automatically in letterbox mode when it 
>> receives 16:9, and our software captures the 4:3 frames at size 704x576. 
> 
> The card does not go into letterbox mode. It's the broadcaster who
> squeezes the 16:9 picture into 432 lines surrounded by 144 black lines.

Let me rephrase to check I understood correctly. In analog TV, there are 
no anamorphic broadcasts. When the WSS (accessible via /dev/vbi, right?) 
states 16:9, then a 16:9 (sic) TV switches to a mode where it crops 2x72 
lines, then stretches the image both horizontally and vertically to fill 
the whole 16:9 screen. Am I correct?

I must admit I have difficulty believing that. Could you give me the 
URLs of sites explaining all that?

> Some fill the chroma part of the black lines with a PALPlus helper
> signal. Although the algorithms to decode PALPlus are well documented in
> ETS 300 731, I have never seen a software implementation.
> 
>> 1. How do I sense from the software that the mode is currently 16:9 or 4:3?
> 
> Some broadcasters use WSS to signal 16:9.
> In Germany some signal 4:3 even on 16:9 shows.
> Read ETSI EN 300 294.
> 
>> 2. How do I setup the bttv so that it does variable anamorphosis instead 
>> of letterboxing? If that is at all possible of course...
> 
> You can't. Bttv can't stretch vertically.
> 
>   Daniel


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Michel Bardiaux
R&D Director
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