uvch264src element fails to work with two C920 devices

[Adrian Pardini]

On 23 September 2014 19:49, Nicolas Dufresne
<nicolas.dufresne at collabora.com> wrote:
> 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.


What I've found is that it depends on the format (H264, mjpeg) and
also if you open the associated audio device.

I don't have right now with me the original code nor the exchanges at
linux-uvc but my experiment ended with us buying more usb controllers.
A brief summary is here:

http://tangopardo.com.ar/2cf7/2013/12/31/debugging-usb3-0-issues-when-dealing-with-usb2-0-devices