Can't see camera `can't open camera by index`

[robotrapta]

On ubuntu22 I plug in a USB camera, and I see it on lsusb, but when I try to access it with framegrab, I get opencv errors like:

[ERROR:0@0.012] global obsensor_uvc_stream_channel.cpp:158 getStreamChannelGroup Camera index out of range
[ WARN:0@0.012] global cap_v4l.cpp:913 open VIDEOIO(V4L2:/dev/video0): can't open camera by index
[ WARN:0@0.012] global obsensor_stream_channel_v4l2.cpp:82 xioctl ioctl: fd=-1, req=-2140645888
[ WARN:0@0.012] global obsensor_stream_channel_v4l2.cpp:138 queryUvcDeviceInfoList ioctl error return: 9
[ WARN:0@0.012] global obsensor_stream_channel_v4l2.cpp:82 xioctl ioctl: fd=-1, req=-2140645888
[ WARN:0@0.012] global obsensor_stream_channel_v4l2.cpp:138 queryUvcDeviceInfoList ioctl error return: 9
[ WARN:0@0.013] global obsensor_stream_channel_v4l2.cpp:82 xioctl ioctl: fd=-1, req=-2140645888
[ WARN:0@0.013] global obsensor_stream_channel_v4l2.cpp:138 queryUvcDeviceInfoList ioctl error return: 9
[ WARN:0@0.013] global obsensor_stream_channel_v4l2.cpp:82 xioctl ioctl: fd=-1, req=-2140645888
[ WARN:0@0.013] global obsensor_stream_channel_v4l2.cpp:138 queryUvcDeviceInfoList ioctl error return: 9
[ WARN:0@0.013] global obsensor_stream_channel_v4l2.cpp:82 xioctl ioctl: fd=-1, req=-2140645888
[ WARN:0@0.013] global obsensor_stream_channel_v4l2.cpp:138 queryUvcDeviceInfoList ioctl error return: 9

[robotrapta]

The simple answer in this case is just permissioning:

sudo usermod -a -G video $USER