From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from out3-smtp.messagingengine.com ([66.111.4.27]:39389 "EHLO out3-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750760AbaCFNE4 (ORCPT ); Thu, 6 Mar 2014 08:04:56 -0500 Received: from compute4.internal (compute4.nyi.mail.srv.osa [10.202.2.44]) by gateway1.nyi.mail.srv.osa (Postfix) with ESMTP id 20F76208E1 for ; Thu, 6 Mar 2014 08:04:52 -0500 (EST) Message-ID: <53187272.6000901@williammanley.net> Date: Thu, 06 Mar 2014 13:04:50 +0000 From: William Manley MIME-Version: 1.0 To: Paulo Assis CC: Linux Media Mailing List Subject: Re: uvcvideo: logitech C920 resets controls during VIDIOC_STREAMON References: <5317ACAC.8000008@williammanley.net> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-media-owner@vger.kernel.org List-ID: On 06/03/14 12:09, Paulo Assis wrote: > Hi, > > 2014-03-05 23:01 GMT+00:00 William Manley : >> Hi All >> >> I've been attempting to use the Logitech C920 with the uvcvideo driver. >> I set the controls with v4l2-ctl but some of them change during >> VIDIOC_STREAMON. My understanding is that the values of controls should >> be preserved. >> [snip] >> The camera does >> have a mode where it would change by itself but that is disabled >> (exposure_auto=1). > > This alone doesn't guarantee that exposure absolute is untouched. > To do so you need to set V4L2_CID_EXPOSURE_AUTO_PRIORITY to 0 and > V4L2_CID_EXPOSURE_AUTO to V4L2_EXPOSURE_MANUAL The behaviour is the same whether exposure_auto_priority is set to 1 or 0. I don't think I've explained myself clearly - the exposure time does not change by itself, apart from during VIDIOC_STREAMON: * When I'm streaming video from the camera it's constant. * When no data is coming from the camera it's constant It's only modified during STREAMON and when I explicitly set it with v4l2-ctl. This doesn't seem like correct behaviour as it breaks the use-case of setting the controls as you want before starting streaming. My workaround is to reset all the controls after calling VIDIOC_STREAMON but this is ugly and you get a few frames at the beginning of the video stream where the settings are set correctly. Thanks Will