Rotate webcam as well as screen (portrait mode)

cameravideoxrandr

TL;DR: Is it possible to rotate by 90 degrees the feed of a built-in screen webcam?

I have 2 screen monitors, one in landscape and one in portrait mode. The webcam is on the "portrait" monitor, the "landscape" monitor doesn't have a rotation capability (so I cannot switch them). The display on the second screen is rotated using xrandr, via arandr. However, the webcam feed is still filming as if there was no physical rotation, which is a problem for videoconferencing. I would like a way to tweak the video feed at driver level so that I can use it in other applications.

I have tried to use v4l2-ctl but I cannot find a "rotate" features (while there are many configuration options for contrast/hue/etc.). I can use

My distribution is Archlinux but I don't think it's relevant here. The portrait screen is a philips 271P4Q. Lsusb output for the integrated webcam:
Bus 001 Device 005: ID 04ca:7054 Lite-On Technology Corp.

If there's nothing to do yet, I would also like to know whom I can report this to, to improve the situation (Xorg developers? Linux kernel devs?).

Thank you for any input on this.

Best Answer

You might be able to do this as described here. Install and modprobe the v4l2loopback module (you may need to compile it) to create a new video device, then copy the webcam video stream to it via ffmpeg:

ffmpeg -f v4l2 -i /dev/video0 -vf transpose=1 -f v4l2 /dev/video1

Related Solutions

Linux – Webcam on Angström

Devices attached to buses such as PCI, PCMCIA and USB have an identifier that uniquely encode the manufacturer and model. Modules that contain drivers for devices attached to these buses contain information about the devices they support, in the form of a list of PCI identifiers, USB identifiers, PCMCIA identifiers, etc. When the kernel detects a device on one of these buses, it tries to load a driver for this particular identifier. More precisely, the kernel tries to load a module called (say) usb:somelongstring where the long string encodes the device's USB identifier. When you compile or install a kernel, the depmod program reads all the module file (.ko) that you have and generates a modules.alias file in /lib/module/$VERSION/ containing lines like

alias usb:somelongstring uvcvideo

It looks like on your system, you have a driver that supports your device but the modules.alias file does not declare the right alias. First, run depmod -a to make sure that this file is up to date.

If, after than, the module is not automatically loaded but does work when it is loaded manually, then what's going on is that you have a slightly more recent model that has an unknown identifier but works with the same driver because it is sufficiently compatible with known models. In that case, report your success to the upstream developer so that the identifier is added to the next version of the driver. In the meantime, add the alias manually. You'll find the long string in /sys/bus/usb/devices/2-2.4.3/modalias. Create a file called /etc/modprobe.d/local-aliases.conf and add the lines

# Microsoft LifeCam Cinema
alias usb:somelongstring uvcvideo

There is a good write-up of modalias in the Arch wiki.

Xrandr – Cannot Rotate Screen with Nvidia

You need to use --rotate in newer versions of xrandr not the -o switch.

Examples

$ xrandr --output LVDS1 --rotate left
$ xrandr --output LVDS1 --rotate right
$ xrandr --output LVDS1 --rotate normal

What's my output?

You can find out your display's name using xrandr without any arguments.

$ xrandr
Screen 0: minimum 320 x 200, current 1440 x 900, maximum 8192 x 8192
LVDS1 connected primary 1440x900+0+0 (normal left inverted right x axis y axis) 303mm x 190mm
   1440x900       60.0*+   50.0  
   1024x768       60.0  
   800x600        60.3     56.2  
   640x480        59.9  
VGA1 disconnected (normal left inverted right x axis y axis)
HDMI1 disconnected (normal left inverted right x axis y axis)
DP1 disconnected (normal left inverted right x axis y axis)
HDMI2 disconnected (normal left inverted right x axis y axis)
HDMI3 disconnected (normal left inverted right x axis y axis)
DP2 disconnected (normal left inverted right x axis y axis)
DP3 disconnected (normal left inverted right x axis y axis)

NVidia cards

With this graphics card you'll likely need to add this to your "Device" section of your xorg.conf file.

Option    "RandRRotation" "True"

You'll have to restart X11 to get this change to take effect. After doing so xrandr you should be able to rotate your display.