skypeforlinux recognises external webcam but gives black screen

I had the same issue and tried a lot of things. I'm using Ubuntu 19.10(eoan), Skype version 8.59.76.73 and libv4l version is 1.16.7-1. My solution to this problem is based on this Ubuntuforums link.

1. Remove skype completely from your system with

   sudo apt-get purge skype*
   

   or

   snap remove skype
   

2. Install the libv4l-dev packages

   sudo apt install libv4l-dev
   

3. Find where the lib4l packages downloaded with the following command,

   find / -iname "*libv4l*" 2>/dev/null
   

4. Re-install the latest version of skypeforlinux preview version from this Skype repository.

5. Reboot your system.

6. With the path for libv4l you found, use the following command to run skypeforlinux

   LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libv4l/v4l2convert.so skypeforlinux
   

I hope this helps, I solved my problem with these steps.

I know of 2 ways to make your webcam work for skypeforlinux.

1. Preload one of the Video For Linux compatibility libraries.

   galiperkin mentioned one of them, v4l2convert.so; if that doesn't work, you can search for the other one, v4l1compat.so, and preload it in your command for starting Skype. For example, if you find that library in /usr/lib/x86_64-linux-gnu/libv4l/, close Skype and try this command to start it again:

   LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libv4l/v4l1compat.so skypeforlinux
   

   If it gives you messages about an incompatible ELF version, you might be loading the 64-bit libraries for a 32-bit Skype, or something like that: search for the other version.

2. Convert exotic webcam output to an accepted format.

   If Skype detects your webcam, but only shows a black rectangle when you open it, then chances are that it just cannot understand the output of the webcam. My own webcam streams in motion jpeg, in a pixel format "yuvj422p" that I never heard of before. Try if ffplay can handle it; if it can, ffmpeg can too, and that might rescue you.

   First list the available inputs

    $ v4l2-ctl --list-devices
   

   My output reads:

    BT878 video (Hauppauge (bt878)) (PCI:0000:05:01.0):
        /dev/video0
        /dev/vbi0
    USB Camera (041e:401f) (usb-0000:00:14.0-11.2):
        /dev/video1
   

   So I select the second one to test:

    $ ffplay -hide_banner -f v4l2 -i /dev/video1
   

   -hide_banner is a convenience parameter, -f v4l2 chooses the demuxer format, -i /dev/video1 my webcam.

   If ffplay handles your webcam well, you can stop it by typing 'q' on it's video window, and then proceed. Install the loopback driver of Video For Linux; you have to do this only once, but you need sudo rights:

    $ sudo apt-get update
    $ sudo apt-get install v4l2loopback-dkms
   

   This puts slightly more than 100kB extra on your disk: the kernel module v4l2loopback. You have to load that into your kernel, another sudo activity:

    $ sudo modprobe v4l2loopback
   

   after which you can immediately detect an extra video input:

    $ v4l2-ctl --list-devices
   

   should now show something like this:

    BT878 video (Hauppauge (bt878)) (PCI:0000:05:01.0):
        /dev/video0
        /dev/vbi0
    USB Camera (041e:401f) (usb-0000:00:14.0-11.2):
        /dev/video1
    Dummy video device (0x0000) (platform:v4l2loopback-000):
        /dev/video2
   

   All that is left to do, is to let ffmpeg take the input from your exotic webcam, convert it to a common format like yuv420p, and output it through the loopback module to the dummy video device. Sounds complicated, but it 's nothing more than this command: input format - input - filter - output format - output

    $ ffmpeg -hide_banner -f v4l2 -i /dev/video1 -vf format=yuv420p -f v4l2 /dev/video2
   

   You can test its working with ffplay again:

    $ ffplay -hide_banner -f v4l2 -i /dev/video2
   

   Note that I am taking the input from the new video device, the dummy; video1 would be occupied while ffmpeg is reading from it.

   I would like to remark that the ff-combo consumes less than 1% of cpu capacity on my 5-year old. If all goes well, stop ffplay by typing 'q' in it's video window, but let ffmpeg continue.

   Now go to your Skype, and in the Audio and Video settings select the loopback device named as above: Dummy video device. If that works well, all that is left to do is to fine tune, and clean up after you. If it does not, I am as sorry as you are.

   Close off ffmpeg when you're ready, by typing q in the terminal it is running in. You might give it another try, and give your good old webcam a virtual update by adding filters to ffmpeg; those can go in additional -vf parameters, or you can add them before or after the format=yuv420p, separated by comma's. Mine needs quite a boost:

    -vf format=yuv420p,spp=quality=3:mode=hard:qp=5,unsharp=3:3:0.7:5:5:-0.5,hqdn3d,eq=saturation=1.8:gamma=1.4
   

   but I am sure you can find your own ffmpeg filters and how to use them. You can try them out with ffplay before adding them to your ffmpeg commandline

   Now you don't want to read this text and type its commands every time you receive or make a Skype call. I've put mine in ~/.bash_aliases as follows, under the alias name videoskype:

    alias videoskype="xterm -e /bin/bash -ic 'sudo modprobe v4l2loopback;echo Ready for video call, press q to stop;ffmpeg -hide_banner -f v4l2 -i /dev/video1 -vf format=yuv420p -f v4l2 /dev/video2;sudo modprobe --remove v4l2loopback'&"
   

   From now on, the single command videoforskype, given in an interactive shell (a normal terminal, or a launcher for something like bash -ic videoskype) will open a terminal that asks for your sudo password to load the loopback module, keeps ffmpeg running until you stop it, and unloads the loopback module.

   Note that the kernel module loader is quite robust: it handles trying to load an already loaded module gracefully. But if you start videoskype again while another instance is running in another terminal, the ffmpeg in the new one can not read from its input, and stops, causing the loopback module to be unloaded and the first ffmpeg to stop as well.

Success!!