Re: (bisected) Logitech C920 (uvcvideo) stutters since 3.9

Sakari Ailus
2014-11-04T11:59:14Z

Hi Grazvydas,

On Tue, Nov 04, 2014 at 01:16:03AM +0200, Grazvydas Ignotas wrote:
> Hi,
>
> On Mon, Nov 3, 2014 at 12:57 AM, Sakari Ailus <sakari.ailus@iki.fi> wrote:
> > Hi Grazvydas,
> >
> > On Sun, Nov 02, 2014 at 04:03:55AM +0200, Grazvydas Ignotas wrote:
> >> There is periodic stutter (seen in vlc, for example) since 3.9 where
> >> the stream stops for around half a second every 3-5 seconds or so.
> >> Bisecting points to 1b18e7a0be859911b22138ce27258687efc528b8 "v4l:
> >> Tell user space we're using monotonic timestamps". I've verified the
> >> problem is there on stock Ubuntu 14.04 kernel, 3.16.7 from kernel.org
> >> and when using media_build.git . The commit does not revert on newer
> >> kernels as that code changed, but checking out a commit before the one
> >> mentioned gives properly working kernel.
> >>
> >> I'm using Logitech C920 which can do h264 compression and playing the
> >> video using vlc:
> >> cvlc v4l2:///dev/video0:chroma=h264:width=1280:height=720
> >
> > I've got Logitech C270 here but I can't reproduce the problem. The frame
> > rate with the above command is really low, around 5. With a smaller
> > resolution it works quite smoothly. The reason might be that the pixel
> > format is still YUYV. The other option appears to be MJPG.
>
> I've tried lower resolution and YUYV with MJPG too, this has the same problem:
> cvlc v4l2:///dev/video0:chroma=h264:width=320:height=240
> cvlc v4l2:///dev/video0:chroma=yuyv:width=320:height=240
>
> >
> > My vlc is of version 2.0.3 (Debian). Which one do you have, and does it use
> > libv4l2?
>
> Mine is 2.1.4, my distro is Ubuntu 14.04. I can see libv4l2.so.0.0.0
> in maps, but I have no idea what it's used for..
>
> > 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?

--
Cheers,

Sakari Ailus
e-mail: sakari.ailus@iki.fi XMPP: sailus@retiisi.org.uk