Multiple webcam issues

[Nicolas Dufresne]

Le lundi 19 juin 2017 à 11:45 -0700, schmidtbag a écrit :
> Nicolas Dufresne-5 wrote
> > please be aware the your are using @yahoo.com emails, which all goes to
> > spam on many systems.
> 
> It actually didn't, but thanks for the heads up anyway.
> 
> 
> > That's a known issue, distributed between the slow firmware in that
> > camera, UVC driver not being very smart, and GStreamer probing all
> > possible feature on the camera before the camera starts.
> > 
> > I have found how to optimize this, but haven't found time (neither anyone
> > to sponsor work). Let me know if you are interested.
> 
> I can't imagine the camera firmware or the UVC driver is entirely the issue,
> considering ffmpeg, VLC, and qv4l2 can all initialize the camera
> instantaneously.  

We are saying the same thing I believe. None of ffmpeg, vlc or qv4l2
implements automatic format negotiation. Also, they don't make any use
of the non-enumerable part of V4L2 like colorimetry and interlacing. To
make a list of all these, you need to do a lot of calls into the
kernel, which on UVC triggers a lot of camera round-trips.

> I am interested in your optimization though.  I intend
> this to record at the push of a button without access to a UI, so the delay
> may be a problem at some point.

Sure, ideally, if you'd like to do that yourself, just come buy on IRC,
I'll be able answer your questions (freenode #gstreamer, I'm ndufresne)
.

> 
> 
> > For live source, the recorded time is includes initial GAPs indeed.
> > That's normal, though there is some proposal on bugzilla to allow
> > clipping that initial delay. 
> > 
> > https://bugzilla.gnome.org/show_bug.cgi?id=750794
> > 
> > ...
> > 
> > "videomixer" could be the wrong choice here, depending on the GStreamer
> > version. In general, to be sure, use compositor.
> 
> Thanks, I'll be sure to try these out when I get home.
> 
> 
> 
> --
> View this message in context: http://gstreamer-devel.966125.n4.nabble.com/Multiple-webcam-issues-tp4683435p4683446.html
> Sent from the GStreamer-devel mailing list archive at Nabble.com.
> _______________________________________________
> gstreamer-devel mailing list
> gstreamer-devel at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/gstreamer-devel
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 181 bytes
Desc: This is a digitally signed message part
URL: <https://lists.freedesktop.org/archives/gstreamer-devel/attachments/20170620/0d7d9b03/attachment.sig>