[linux-dvb] Re: More V4 Video API Q's

[Rob.McConnell@Zarlink.Com]

Hi Marcus,

I haven't been ignoring you, but have been trying to get my head around the
V4L2 spec and how maybe we could use it on STB products.

First of all, do you know whether anyone out there actually uses the V4L2
spec for STB hardware?

Marcus Metzler <mocm@mocm.de> wrote on 27/09/2004 15:39:26:

> >>>>> "Rob" == Rob McConnell <Rob.McConnell@Zarlink.Com> writes:
>
>     Rob> Hi Folks,
>
>     Rob> Been looking at the video driver a bit more and have the
>     Rob> following points to make:
>
>     Rob> 1) Most STB hardware has a video decoder and video scaler
>     Rob> (either in one block or two).  Now, the current V4 API
>     Rob> doesn't handle requests to size the screen to say 1/4 size,
>     Rob> or 1/16 size or 2x size _and_ to position it.  I think we
>     Rob> should add these to the existing video.h header file and add
>     Rob> a capabilities flag to check whether the underlying hardware
>     Rob> can scale and position the video.  This would be preferred
>     Rob> over having a separate video scaler API and device node.
>
>     Rob> Could we extend dvb_video_presentation_format?
>
> That is usually handled by the v4l1/2 API.

Now I'm not sure what type of V4L device we should use for this (capture,
overlay, output, ...) and also do we want to deviate from the source->sink
approach of connecting devices up in the V4 API?  Currently, we can set the
source of the video decoder to be from a demux fd, but there's no similar
method of connecting a video fd to a V4L2 device, or is there?

Also, looking at the V4L2 0.7 API it seems that the /dev/vout device is
still WIP in terms of assigning minor numbers, etc.  Is this really the
case?

Then there's the story of the video encoder (DENC).  AFAICT, the V4L/V4L2
API doesn't support things like enabling/disabling Macrovision, CGMS
enabling/disabling and turning on/off test patterns (e.g. colour bars). If
it can, then maybe it might be worth using this API.  However, I think it
might just be as simple to knock up a denc.h V4 API that incorporates video
output encoder features as well as including the vbi.h file for WSS/VPS/TTX
insertion into the VBI.

I think the _real_ question is how close are the V4L2 and Linux DVB APIs
and are they starting to merge?  Would it be better to have a
"self-contained" set of Linux DVB APIs that handle most STB h/w
requirements (as well as cards) or should there be some cross-pollination
going on?

Any suggestions/thoughts would be most welcome.

Cheers,

Rob : )