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

Rémi Denis-Courmont
2014-11-04T20:41:47Z

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