Re: Grabbing 4:3 and 16:9
- Date: Tue, 26 Feb 2008 17:55:53 +0100
- From: Michel Bardiaux <mbardiaux@xxxxxxxxxxx>
- Subject: Re: Grabbing 4:3 and 16:9
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
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