On Fri, Jun 21, 2019 at 04:07:25PM +0200, Seba Kerckhof wrote:
> Under Debian 10 rc1, when I plug in my USB camera (the very common logitech
> c930e), 2 devices are added (e.g. /dev/video0 and /dev/video1).
>
> v4l-info works on /dev/video0, but fails on /dev/video1
> (VIDIOC_G_FMT(VIDEO_CAPTURE): Invalid argument). When I try to access the
> device using gstreamer it tells me that /dev/video1 is not a capture device.
This is the feature added in commit 088ead25524583e2200aa99111bea2f66a86545a.
media: uvcvideo: Add a metadata device node
Some UVC video cameras contain metadata in their payload headers. This
patch extracts that data, adding more clock synchronisation information,
on both bulk and isochronous endpoints and makes it available to the user
space on a separate video node, using the V4L2_CAP_META_CAPTURE capability
and the V4L2_BUF_TYPE_META_CAPTURE buffer queue type. By default, only the
V4L2_META_FMT_UVC pixel format is available from those nodes. However,
cameras can be added to the device ID table to additionally specify their
own metadata format, in which case that format will also become available
from the metadata node.
Guennadi, sorry but this feels more like a bug than a feature to me, and at
least three other people have reported it as a bug without working out the cause.
* https://bugs.debian.org/930860
* https://bugzilla.kernel.org/show_bug.cgi?id=199193
* https://bugzilla.kernel.org/show_bug.cgi?id=199575
Seba, thanks for reporting this. I met this feature while working on a
closed-source application, added a workaround to ignore cameras that don't
support normal video capture, and haven't yet got round to replying to the
Bugzilla reports above. I'd be happy if someone else took on that task.
BR,
Steve