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

Grazvydas Ignotas
2014-11-17T15:36:04Z

On Thu, Nov 6, 2014 at 12:29 AM, Grazvydas Ignotas <notasas@gmail.com> wrote:
> On Wed, Nov 5, 2014 at 4:05 PM, Laurent Pinchart
> <laurent.pinchart@ideasonboard.com> wrote:
>> Hi Rémi,
>>
>> On Tuesday 04 November 2014 22:41:44 Rémi Denis-Courmont wrote:
>>> 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.
>>
>> Would you be able to capture images from the C920 using yavta, with the
>> uvcvideo trace parameter set to 4096, and send me both the yavta log and the
>> kernel log ? Let's start with a capture sequence of 50 to 100 images.
>
> I've done 2 captures, if that helps:
> http://notaz.gp2x.de/tmp/c920_yavta/
>
> The second one was done using low exposure setting, which allows
> camera to achieve higher frame rate.

So, has anyone had time to look at these?

Gražvydas