uvch264src element fails to work with two C920 devices

[Nicolas Dufresne]

Le 2014-09-23 17:28, Juan Robles a écrit :
> That's weird, since I have both cameras working on the same device 
> using cvlc.
> In this case, the only difference is that with cvlc I can't request a 
> specific bitrate and fallbacks to the default, but otherwise, it works 
> flawlessly.
>
> Isn't it meaningful that having an uvch264src0 it should map to 
> v4l2src0 and the second one, uvch264src1 should map to v4l2src1?
>
> Anyway, tomorrow I'll be attaching them to another device with two usb 
> buses and see if that makes a difference.

I've ran the same test here on Odroid U2, same results (with kernel 
trace "uvcvideo: Failed to submit URB 0 (-28)."). Whenever a mjpeg muxed 
stream is requested, the second stream fails, so Adrian theory is quite 
plausible. If you try getting two H264 streams this way:

gst-launch-1.0 v4l2src device=/dev/video1 ! video/x-h264,width=1280 ! 
fakesink

that works. Most likely that cvlc is not using this UVC extended API 
(and the reason why bitrate can't be selected), but I might be wrong on 
that.

Nicolas