Webcam setup - ArchWiki

# Webcam setup

From ArchWiki

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

Identify the name of your webcam (using, for example, `lsusb`) and find a proper driver. See Webcam devices for the details about drivers.

Add your webcam's kernel module in `/etc/modules-load.d/webcam.conf` so it will be loaded into the kernel during init stage bootstrapping.

If your webcam is USB, the kernel should automatically load the proper driver. If this is the case, check dmesg after you plug your 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

## 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 (qv4l2), available in the package v4l-utils. Just install it and launch, and it will present you a list of configurable settings. Changing these settings will affect all applications.

## Applications

See also List of applications/Multimedia#Webcam.

### xawtv

This is a basic v4l 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 it (xawtv) and run it with:

    $ xawtv -c /dev/video0

If you are using an nVidia graphic card, and you 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

### 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 v4l:// :v4l-vdev="/dev/video0" :v4l-adev="/dev/audio2"

This will make VLC mirror your webcam. To take stills, simply choose 'Snapshot' in the 'Video' menu. To record the stream, you add a `--sout` argument, 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.) Notice that this will not produce a mirror on the display - in order to see what you are recording, you would need to add the display as a destination to the argument:

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

(Though this can tax older hardware somewhat...)

### 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 your current folder as shotXXXX.png. If you want to record continuous video:

    $ 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.

### mpv

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

    $ mpv av://v4l2:/dev/video0

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

### 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.

### 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.

### 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.

Category:

- Imaging