Em Sáb, 2005-09-10 às 18:44 -0700, Andrew Morton escreveu:
> Mauro Carvalho Chehab <[email protected]> wrote:
> >
> > - adds all defines, ioctls and structs needed for the sliced VBI API
> >
>
> What is "sliced VBI"?
Sorry for this... it is too much video jargon :-)
VBI = Vertical Blank Interval.
It is related with the way TV signals does work. It sends a line, then,
it has a retrace time to allow the tube to move electrons to the
beginning of the next line. This was the main reason at the beginning of
analog B&W TV.
There are a lot of bandwidth lost on VBI. So, lots of TV systems uses
it to send other informations, like Closed Capture and Teletext. Also,
broadcasters uses this as a channel to exchange information from the
content producer to their subsidiaries at each city.
There's already a raw VBI interface on V4L2 api, used for Closed
Captions and Teletext. The decoding is doing at userlevel space and it
is mostly for analog TV signals, non encoded.
Encoded signals (MPEG, for example), may need also to transmit other
informations (like, for example, display aspect, i.e. 4x3,
widescreen...). Sliced VBI interface is a method to allow the video
stream to transmit this kind of information.
>
Cheers,
Mauro.
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