[linux-dvb] Re: Video output support for cards and STBs

[Rob.McConnell@Zarlink.Com]

Hi Guys,

Johannes Stezenbach <js@linuxtv.org> wrote on 05/10/2004 22:07:41:
> Rob.McConnell@Zarlink.Com wrote:
> > Now a DENC on a STB/iDTV can have some or all of these functions:
> >
> > 1) Ability to set the video standard for composite output (e.g. PAL
> > B/G/H/I/M/N, NTSC-M/J, PAL-CN, SECAM, etc.)
>
> Hm, I thought the PAL and NTSC variants differ only in the sound
> carrier frequencies, so it is only relevant for modulated VHF/UHF output.
> If so, it is not really appropriate to handle this in DirectFB, is it?

Well, take NTSC M/J for example.  The difference here is the black level.
If we start to look at the different flavours of PAL (B/G/H/N/M/CN/I) then
the differences lie in the chroma sub-carrier frequency as well as the
video bandwidth.  Then if you look at NTSC/PAL you see that there a
different number of lines in the signal (525/625).

>
> > 2) Ability to set the video output mode (e.g. RGB - with/without sync
on
> > green, component video - YUV, S-VHS - Y/C and composite - CVBS).
>
> In Galaxis' current STBs this is handled via an external
> AV-mux, controlled by a (trivial) proprietary API. But we
> should maybe add a standardized API for it to DFB or DVB.

True.  If a DENC can output multiple video "flavours" (RGB, Y/C, CVBS)
simultaneously, then you need some mux to select the one you want to output
on say SCART1.  However, if you say that we have N virtual DENCs where each
one can provide a single video output signal (with the ability to set the
output mode), then this would solve this problem.  Also, it would be akin
to how we have multiple frontend devices and virtual demux devices in the
Linux DVB V4 API.

> All VBI stuff could trivially be added to the existing DVB VBI API.
> IMHO DirectFB has nothing to do with it (it controls other
> functions of the video output encoder).

I'm happy with extending the vbi.h to add more VBI functionality. : )

> An even more fundamental question: Should we even care about
> supporting STBs which do not use DirectFB, or just say "sorry, Rob".

That goes against the freedom of using open source software and allowing
the "user" to decide (rightly or wrongly) what s/w he/she wants to use.
;^)

Rob : )