Messages in this thread | | | Date | Mon, 31 Aug 2009 07:55:50 +0200 | From | Németh Márton <> | Subject | Re: [RESEND][PATCH 1/2] v4l2: modify the webcam video standard handling |
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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@freemail.hu> escreveu: > >> From: Márton Németh <nm127@freemail.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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