Webcam setup - ArchWiki

# Webcam setup

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This is a guide to setting up your webcam in Arch Linux.

Most probably your webcam will work out of the box. Permissions to access video devices (e.g. `/dev/video0`) are handled by udev, there is no configuration necessary.

## Loading

Most recent webcams are UVC (USB Video Class) compliant and are supported by the generic uvcvideo kernel driver module. To check that your webcam is recognized, run dmesg just after you plug the webcam in. You should see something like this:

    # dmesg | tail

    sn9c102: V4L2 driver for SN9C10x PC Camera Controllers v1:1.24a
    usb 1-1: SN9C10[12] PC Camera Controller detected (vid/pid 0x0C45/0x600D)
    usb 1-1: PAS106B image sensor detected
    usb 1-1: Initialization succeeded
    usb 1-1: V4L2 device registered as /dev/video0
    usb 1-1: Optional device control through 'sysfs' interface ready
    usbcore: registered new driver sn9c102

Some pre-UVC webcams are also supported via the gspca kernel driver module. See the gspca devices for a non-exhaustive list of supported devices under this framework.

Otherwise, if your webcam is not supported by the kernel's drivers, an external driver is necessary. The first step is to identify the name of the webcam, using for example `lsusb`. Then you can check webcam devices for information and resources about webcams. Once you find a driver compatible with the webcam, you have to add the corresponding kernel module in `/etc/modules-load.d/webcam.conf` so it will be loaded into the kernel during init stage bootstrapping.

Note: The Linux kernel to userspace API used to control webcams is named Video4Linux2, v4l2 for short. All applications which support v4l2 will work with the kernel's drivers.

## Configuration

If you want to configure brightness, color and other webcam parameters (e.g. in the case when out-of-the-box colors are too bluish/reddish/greenish) you may use Qt V4L2 Test Bench. To run it, install v4l-utils and launch `qv4l2`, and it will present you a list of configurable settings. Changing these settings will affect all applications.

### Command line

v4l-utils also installs an equivalent command line tool, `v4l2-ctl`. To list all video devices:

    $ v4l2-ctl --list-devices

To list the configurable settings of a video device:

    $ v4l2-ctl -d /dev/video0 --list-ctrls

### Persisting configuration changes

Configuration made via V4L2 does not persist after the webcam is disconnected and reconnected. It's possible to use `v4l2-ctl` with Udev rules in order to set some configuration each time a particular camera is connected.

For example, to set a default zoom setting on a particular Logitech webcam each time it is connected, add a udev rule like this:

    /etc/udev/rules.d/99-logitech-default-zoom.rules

    SUBSYSTEM=="video4linux", KERNEL=="video[0-9]*", ATTRS{product}=="HD Pro Webcam C920", ATTRS{serial}=="BBBBFFFF", ATTR{index}=="0", RUN+="/usr/bin/v4l2-ctl -d $devnode --set-ctrl=zoom_absolute=170"

To find udev attributes like the product name and serial, see Udev#List the attributes of a device. It also possible to set a static name for a video device).

## Applications

See also List of applications/Multimedia#Webcam.

### xawtv

This is a basic Video4Linux2 device viewer, and although it is intended for use with TV tuner cards, it works well with webcams. It will display what your webcam sees in a window.

Install xawtv and run it with:

    $ xawtv -c /dev/video0

In case of error see #xawtv with nvidia card.

### VLC

VLC can also be used to view and record your webcam. In VLC's "Media" menu, open the 'Capture Device...' dialog and enter the video and audio device files. Or from the command line, do:

    $ vlc v4l2://:input-slave=alsa://:v4l-vdev="/dev/video0"

This will make VLC mirror your webcam.

- To take stills, simply choose Snapshot in the Video menu.
- To record the stream, add a `--sout` argument to the command line, e.g.

    $ vlc v4l://:v4l-vdev="/dev/video0":v4l-adev="/dev/audio2" --sout "#transcode{vcodec=mp1v,vb=1024,scale=1,acodec=mpga,ab=192,channels=2}:duplicate{dst=std{access=file,mux=mpeg1,dst=/tmp/test.mpg}}"

(Obviously a bit overkill with regard to the bit rates but it is fine for testing purposes). Note that by default this will not display the video, in order to see what you are recording, you need to add the display as a destination to the argument (note that it will slow down the operation):

    ... :duplicate{dst=display,dst=std{access= ....

If VLC does not detect webcams, ensure that zvbi package is installed.

### MPlayer

To use MPlayer to take snapshots from your webcam run this command from the terminal:

    $ mplayer tv:// -tv driver=v4l2:width=640:height=480:device=/dev/video0 -fps 15 -vf screenshot

From here you have to press `s` to take the snapshot. The snapshot will be saved in the current folder as `shotXXXX.png`. If you want to record video continuous:

    $ mencoder tv:// -tv driver=v4l2:width=640:height=480:device=/dev/video0:forceaudio:adevice=/dev/dsp -ovc lavc -oac mp3lame -lameopts cbr:br=64:mode=3 -o filename.avi

Press `Ctrl+c` to end the recording.

To play video with MPlayer using MJPEG as the pixelformat instead of the default, which in most cases is YUYV, you can run the following:

    $ mplayer tv:// -tv driver=v4l2:width=640:height=480:device=/dev/video0:outfmt=mjpeg -fps 15

### mpv

To use mpv to take snapshots from your webcam, run this command from the terminal:

    $ mpv av://v4l2:/dev/video0 --profile=low-latency --untimed

From here you have to press `s` to take the snapshot. The snapshot will be saved in your current folder as `mpv-shotNNNN.jpg`.

To use MJPEG as the pixelformat instead of the default, which in most cases is YUYV, you can run the following instead:

    $ mpv --demuxer-lavf-format=video4linux2 --demuxer-lavf-o-set=input_format=mjpeg av://v4l2:/dev/video0

In some cases this can lead to drastic improvements in quality and performance (5FPS -> 30FPS for example).

To adjust webcam settings, including the resolution, see the mpv documentation.

### FFmpeg

See FFmpeg#Recording webcam.

## Troubleshooting

### V4L1 support

Version 2.6.27 of the Linux kernel dropped support for the legacy Video4Linux (1) API. Pixel format decoding has been pushed to user space, since Video4Linux version 2 does not support kernel space decoding. The libv4l library provides userland applications with pixel decoding services and will be used by most programs. Other compatibility layers are also available.

If your device is created but your image looks strange (e.g. nearly completely green), you probably need this.

If the application has V4L2 support but no pixelformat support then use the following command:

    LD_PRELOAD=/usr/lib/libv4l/v4l2convert.so application

If the application only supports the older version of V4L, use this command:

    LD_PRELOAD=/usr/lib/libv4l/v4l1compat.so application

Tip: You also might want to put a line like the following into `/etc/profile` or xprofile so you do not have to type that long command all the time: `export LD_PRELOAD=/usr/lib/libv4l/v4l2convert.so` or `export LD_PRELOAD=/usr/lib/libv4l/v4l1compat.so`

For 32-bit multilib applications, install the lib32-v4l-utils package and replace `/usr/lib/libv4l/` by `/usr/lib32/libv4l/` in the above commands.

### xawtv with nvidia card

If you are using an nvidia graphic card, and get an error like

    X Error of failed request:  XF86DGANoDirectVideoMode
     Major opcode of failed request:  139 (XFree86-DGA)
     Minor opcode of failed request:  1 (XF86DGAGetVideoLL)
     Serial number of failed request:  69
     Current serial number in output stream:  69

you should instead run it as `$ xawtv -nodga`

### Microsoft Lifecam Studio/Cinema

Under certain configurations, the Microsoft lifecam studio/cinema may request too much usb bandwidth and fail see Uvcvideo FAQ. In this case, change the buffering by loading the `uvcvideo` driver with `quirks=0x80`. Add it to `/etc/modprobe.d/uvcvideo.conf` :

    /etc/modprobe.d/uvcvideo.conf

    ## fix bandwidth issue for lifecam studio/cinema
    options uvcvideo quirks=0x80

Note: If delays are visible in the logs, or the camera works periodically, this workaround should apply generally. Bigger values such as `quirks=0x100` are possible.

### Skype

When testing the webcam, note the following:

- The echobot does not support videochat. Do not use it for testing your webcam.
- Skype might recognize different video/camera devices (/dev/video*). These will be listed as something like "integrated camera..." in a dropdown menu in the camera settings. Try each camera and wait a few seconds, because it takes time to switch to a different camera.

### Check bandwidth used by USB webcams

When running multiple webcams on a single USB bus, they may saturate the bandwidth of the USB bus and not work properly. You can diagnose this with the usbtop tool from the usbtopAUR package.

### Invert the video stream

If your video stream is inverted, you can make a new virtual video camera which inverts the inverted video. You need to install v4l-utils and also v4l2loopback-dkms. Create the virtual video camera:

    # modprobe v4l2loopback

Check the name of the newly created camera:

    $ v4l2-ctl --list-devices
    Dummy video device (0x0000) (platform:v4l2loopback-000):
       	/dev/video1

Then you can run ffmpeg to read from your actual webcam (here `/dev/video0`) and invert it and feed it to the virtual camera:

    $ ffmpeg -f v4l2 -i /dev/video0 -vf "vflip" -f v4l2 /dev/video1

You can use the "Dummy" camera in your applications instead of the "Integrated" camera.

### Bad image quality

If you experience images being too bright, too dark, too exposed or any other, you can install v4l2ucpAUR to tweak your image output.

Category:

- Digital imaging