linux-kernel - Re: [RESEND][PATCH 1/2] v4l2: modify the webcam video standard handling

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Date:	Mon, 31 Aug 2009 07:55:50 +0200
From:	Németh Márton <nm127@...email.hu>
To:	Mauro Carvalho Chehab <mchehab@...radead.org>
CC:	Jean-Francois Moine <moinejf@...e.fr>,
	Thomas Kaiser <thomas@...ser-linux.li>,
	linux-media@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RESEND][PATCH 1/2] v4l2: modify the webcam video standard handling

Hi,

first of all thank you for your detailed answer.

Mauro Carvalho Chehab wrote:
> Hi Németh,
> 
> Em Sun, 23 Aug 2009 11:30:42 +0200
> Németh Márton <nm127@...email.hu> escreveu:
> 
>> From: Márton Németh <nm127@...email.hu>
>>
>> Change the handling of the case when vdev->tvnorms == 0.
>>
> 
> This patch (together with a few others related to tvnorms and camera drivers)
> reopens an old discussion: should webcams report a tvnorm?
> 
> There's no easy answer for it since:
> 
> 1) removing support for VIDIOC_G_STD/VIDIOC_S_STD causes regressions, since
> some userspace apps stops working;
> 
> 2) It is a common scenario to use cameras connected to some capture only devices
> like several bttv boards used on surveillance systems. Those drivers report STD,
> since they are used also on TV;
> 
> 3) There are even some devices that allows cameras to be connected to one input and
> TV on another input. This is another case were the driver will report a TV std;
> 
> 4) Most webcam formats are based on ITU-T formats designed to be compatible
> with TV (formats like CIF and like 640x480 - and their multiple/sub-multiples);
> 
> 5) There are formats that weren't originated from TV on some digital webcams,
> so, for those formats, it makes no sense to report an existing std.
> 
> Once people proposed to create an special format for those cases
> (V4L2_STD_DIGITAL or something like that), but, after lots of discussions,
> no changes were done at API nor at the drivers.
> 
> While we don't have an agreement on this, I don't think we should apply a patch
> like this.

I was reading the V4L2 specification and based my patch on the specification.

Maybe the specification is wrong at that point? (see Chapter 1.7 Video Standards
at http://v4l2spec.bytesex.org/spec/x448.htm , starting with paragraph 6:
"Special rules apply to USB cameras...")

Regards,

	Márton Németh

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