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

[Grazvydas Ignotas <notasas@gmail.com>]

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.

-- 
Gražvydas