From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from ns207790.ip-94-23-215.eu ([94.23.215.26]:43545 "EHLO ns207790.ip-94-23-215.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751188AbaKDUlr convert rfc822-to-8bit (ORCPT ); Tue, 4 Nov 2014 15:41:47 -0500 From: =?ISO-8859-1?Q?R=E9mi?= Denis-Courmont To: Sakari Ailus Cc: Grazvydas Ignotas , linux-media@vger.kernel.org, Laurent Pinchart , Hans Verkuil Subject: Re: (bisected) Logitech C920 (uvcvideo) stutters since 3.9 Date: Tue, 04 Nov 2014 22:41:44 +0200 Message-ID: <36286542.DzZr56uF9K@basile.remlab.net> In-Reply-To: References: <20141104115839.GN3136@valkosipuli.retiisi.org.uk> MIME-Version: 1.0 Content-Transfer-Encoding: 8BIT Content-Type: text/plain; charset="utf-8" Sender: linux-media-owner@vger.kernel.org List-ID: Le mardi 04 novembre 2014, 15:42:37 Rémi Denis-Courmont a écrit : > Le 2014-11-04 14:58, Sakari Ailus a écrit : > >> > Have you tried with a different application to see if the problem > >> > >> persists? > >> > >> Tried mplayer and cheese now, and it seems they are not affected, so > >> it's an issue with vlc. I wonder why it doesn't like newer flags.. > >> > >> Ohwell, sorry for the noise. > > > > I guess the newer VLC could indeed pay attention to the monotonic > > timestamp > > flag. Remi, any idea? > > VLC takes the kernel timestamp, if monotonic, since version 2.1. > Otherwise, it generates its own inaccurate timestamp. So either that > code is wrong, or the kernel timestamps are. >>From a quick check with C920, the timestamps from the kernel are quite jittery, and but seem to follow a pattern. When requesting a 10 Hz frame rate, I actually get a frame interval of about 8/9 (i.e. 89ms) jumping to 1/3 every approximately 2 seconds. >>From my user-space point of view, this is a kernel issue. The problem probably just manifests when both VLC and Linux versions support monotonic timestamps. Whether the root cause is in the kernel, the device driver or the firmware, I can´t say. -- Rémi Denis-Courmont http://www.remlab.net/