On Fri, Mar 17, 2017 at 01:02:07PM +0100, Philipp Zabel wrote:

I think most of the simple, fixed pipeline use cases could be handled by
libv4l2, by allowing to pass a v4l2 subdevice path to v4l2_open. If that
function internally would set up the media links to the
nearest /dev/video interface, propagate format, resolution and frame
intervals if necessary, and return an fd to the video device, there'd be
no additional complexity for the users beyond selecting the v4l2_subdev
instead of the video device.

... which would then require gstreamer to be modified too. The gstreamer
v4l2 plugin looks for /dev/video* or /dev/v4l2/video* devices and monitors
these for changes, so gstreamer applications know which capture devices
are available:

  const gchar *paths[] = { "/dev", "/dev/v4l2", NULL };
  const gchar *names[] = { "video", NULL };

  /* Add some depedency, so the dynamic features get updated upon changes in
   * /dev/video* */
  gst_plugin_add_dependency (plugin,
      NULL, paths, names, GST_PLUGIN_DEPENDENCY_FLAG_FILE_NAME_IS_PREFIX);

I haven't checked yet whether sys/v4l2/gstv4l2deviceprovider.c knows
anything about the v4l2 subdevs.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
according to speedtest.net.