Virtual camera on OBS-Studio not working

[Paul Smith]

Dear All,

I have upgraded from F33 to F34. Everything is working fine now except
the OBS-Studio virtual camera, which is not working.

I am using v4l2loopback, and I see that my camera lights up when I
open OBS-Studio, but suddenly it goes off.

There is no problem with my camera, as it works fine on Skype, for instance.

Any ideas?

Thanks in advance,

Paul

[Jonathan Billings]

On Apr 28, 2021, at 12:54, Paul Smith  wrote:
> Dear All,
>
> I have upgraded from F33 to F34. Everything is working fine now except
> the OBS-Studio virtual camera, which is not working.
>
> I am using v4l2loopback, and I see that my camera lights up when I
> open OBS-Studio, but suddenly it goes off.
>
> There is no problem with my camera, as it works fine on Skype, for instance.

I don’t believe that v4l2loopback is part of Fedora, are you sure the kernel module is being compiled?  Does it use dkms?

—
Jonathan Billings

[Paul Smith]

On Thu, Apr 29, 2021 at 1:38 AM Jonathan Billings  wrote:
> > I have upgraded from F33 to F34. Everything is working fine now except
> > the OBS-Studio virtual camera, which is not working.
> >
> > I am using v4l2loopback, and I see that my camera lights up when I
> > open OBS-Studio, but suddenly it goes off.
> >
> > There is no problem with my camera, as it works fine on Skype, for instance.
>
> I don’t believe that v4l2loopback is part of Fedora, are you sure the kernel module is being compiled?  Does it use dkms?

Thanks, Jonathan. I meanwhile installed the v4l2loopback-dkms package from

https://copr.fedorainfracloud.org/coprs/sentry/v4l2loopback/

and reboot, but the problem persists.

Any further ideas?

Paul

[Jonathan Billings]

On Thu, Apr 29, 2021 at 11:31:05AM +0100, Paul Smith wrote:
> Thanks, Jonathan. I meanwhile installed the v4l2loopback-dkms package from
>
> https://copr.fedorainfracloud.org/coprs/sentry/v4l2loopback/
>
> and reboot, but the problem persists.

I'd check the dkms build logs in:

/var/lib/dkms/v4l2loopback/${V4L2LOOPBACK_VERSION}/build/make.log

(replace ${V4L2LOOPBACK_VERSION} with the version you have installed,
it looks like it is 0.12.5 from the repo)

Looking at the issues in the upstream git repo, it appears to be an
issue with the version of GCC not matching the one used to build the
kernel.  The suggestions were to run 'dnf downgrade gcc' before
building.  Not sure if that helps.

See this closed issue:
https://github.com/umlaeute/v4l2loopback/issues/410

[Paul Smith]

On Thu, Apr 29, 2021 at 1:25 PM Jonathan Billings  wrote:
> > Thanks, Jonathan. I meanwhile installed the v4l2loopback-dkms package from
> >
> > https://copr.fedorainfracloud.org/coprs/sentry/v4l2loopback/
> >
> > and reboot, but the problem persists.
>
> I'd check the dkms build logs in:
>
> /var/lib/dkms/v4l2loopback/${V4L2LOOPBACK_VERSION}/build/make.log
>
> (replace ${V4L2LOOPBACK_VERSION} with the version you have installed,
> it looks like it is 0.12.5 from the repo)
>
> Looking at the issues in the upstream git repo, it appears to be an
> issue with the version of GCC not matching the one used to build the
> kernel.  The suggestions were to run 'dnf downgrade gcc' before
> building.  Not sure if that helps.
>
> See this closed issue:
> https://github.com/umlaeute/v4l2loopback/issues/410

Thanks, Jonathan. Can you detect any problem in the make.log:

------------------------------
# more  /var/lib/dkms/v4l2loopback/0.12.5/5.11.16-300.fc34.x86_64/x86_64/log/make.log
DKMS make.log for v4l2loopback-0.12.5 for kernel 5.11.16-300.fc34.x86_64 (x86_64
)
Thu Apr 29 09:21:31 AM WEST 2021
Building v4l2-loopback driver...
make -C /lib/modules/5.11.16-300.fc34.x86_64/build M=/var/lib/dkms/v4l2loopback/
0.12.5/build modules
make[1]: Entering directory '/usr/src/kernels/5.11.16-300.fc34.x86_64'
  CC [M]  /var/lib/dkms/v4l2loopback/0.12.5/build/v4l2loopback.o
  MODPOST /var/lib/dkms/v4l2loopback/0.12.5/build/Module.symvers
  CC [M]  /var/lib/dkms/v4l2loopback/0.12.5/build/v4l2loopback.mod.o
  LD [M]  /var/lib/dkms/v4l2loopback/0.12.5/build/v4l2loopback.ko
  BTF [M] /var/lib/dkms/v4l2loopback/0.12.5/build/v4l2loopback.ko
Skipping BTF generation for /var/lib/dkms/v4l2loopback/0.12.5/build/v4l2loopback
.ko due to unavailability of vmlinux
make[1]: Leaving directory '/usr/src/kernels/5.11.16-300.fc34.x86_64'
#
------------------------------

Paul

[Jonathan Billings]

On Thu, Apr 29, 2021 at 01:36:13PM +0100, Paul Smith wrote:
> Thanks, Jonathan. Can you detect any problem in the make.log:
>
> # more  /var/lib/dkms/v4l2loopback/0.12.5/5.11.16-300.fc34.x86_64/x86_64/log/make.log
> DKMS make.log for v4l2loopback-0.12.5 for kernel 5.11.16-300.fc34.x86_64 (x86_64
> )
> Thu Apr 29 09:21:31 AM WEST 2021
> Building v4l2-loopback driver...
> make -C /lib/modules/5.11.16-300.fc34.x86_64/build M=/var/lib/dkms/v4l2loopback/
> 0.12.5/build modules
> make[1]: Entering directory '/usr/src/kernels/5.11.16-300.fc34.x86_64'
>   CC [M]  /var/lib/dkms/v4l2loopback/0.12.5/build/v4l2loopback.o
>   MODPOST /var/lib/dkms/v4l2loopback/0.12.5/build/Module.symvers
>   CC [M]  /var/lib/dkms/v4l2loopback/0.12.5/build/v4l2loopback.mod.o
>   LD [M]  /var/lib/dkms/v4l2loopback/0.12.5/build/v4l2loopback.ko
>   BTF [M] /var/lib/dkms/v4l2loopback/0.12.5/build/v4l2loopback.ko
> Skipping BTF generation for /var/lib/dkms/v4l2loopback/0.12.5/build/v4l2loopback
> .ko due to unavailability of vmlinux
> make[1]: Leaving directory '/usr/src/kernels/5.11.16-300.fc34.x86_64'
> #

That looks like it built OK.  Does 'sudo dkms status v4l2loopback' say
everything is OK?

[Paul Smith]

On Thu, Apr 29, 2021 at 1:45 PM Jonathan Billings  wrote:
> That looks like it built OK.  Does 'sudo dkms status v4l2loopback' say
> everything is OK?

It seems OK, Jonathan:

$ sudo dkms status v4l2loopback
[sudo] password for x:
v4l2loopback, 0.12.5, 5.11.16-300.fc34.x86_64, x86_64: installed
(original_module exists)
$

Paul

[Paul Smith]

On Thu, Apr 29, 2021 at 1:47 PM Paul Smith  wrote:
> > That looks like it built OK.  Does 'sudo dkms status v4l2loopback' say
> > everything is OK?
>
> It seems OK, Jonathan:
>
> $ sudo dkms status v4l2loopback
> [sudo] password for x:
> v4l2loopback, 0.12.5, 5.11.16-300.fc34.x86_64, x86_64: installed
> (original_module exists)
> $

But when I go to OBS-Studio to configure

Video capture device (V4L2),

only my physical appears listed:

Easy camera 5M.

If I select that camera, I do not get any video on OBS-Studio.

Can the problem be caused by OBS-Studio?

Paul

[Jonathan Billings]

On Thu, Apr 29, 2021 at 01:47:32PM +0100, Paul Smith wrote:
> It seems OK, Jonathan:
>
> $ sudo dkms status v4l2loopback
> [sudo] password for x:
> v4l2loopback, 0.12.5, 5.11.16-300.fc34.x86_64, x86_64: installed
> (original_module exists)
> $

That 'original_module exists' means that there's already another
package providing the driver.  I wonder if you have conflicting
installs of the package from copr and the one in rpmfusion?

Is the v4l2loopback kernel module loaded?  Do you see it in the output
of 'lsmod'?  Can you run 'modprobe v4l2loopback'?  Is there anything
in the kernel 'dmesg' after you load it?

[Paul Smith]

On Thu, Apr 29, 2021 at 1:58 PM Jonathan Billings  wrote:
> > $ sudo dkms status v4l2loopback
> > [sudo] password for x:
> > v4l2loopback, 0.12.5, 5.11.16-300.fc34.x86_64, x86_64: installed
> > (original_module exists)
> > $
>
> That 'original_module exists' means that there's already another
> package providing the driver.  I wonder if you have conflicting
> installs of the package from copr and the one in rpmfusion?
>
> Is the v4l2loopback kernel module loaded?  Do you see it in the output
> of 'lsmod'?  Can you run 'modprobe v4l2loopback'?  Is there anything
> in the kernel 'dmesg' after you load it?

The answers to all your questions is YES, but 'dmesg' returns the following:

---------------------------
[  263.923694] EDAC amd64: Node 0: DRAM ECC disabled.
[  265.686950] systemd-sysv-generator[37295]: SysV service
'/etc/rc.d/init.d/livesys' lacks a native systemd unit file.
Automatically generating a unit file for compatibility. Please update
package to include a native systemd unit file, in order to make it
more safe and robust.
[  265.686995] systemd-sysv-generator[37295]: SysV service
'/etc/rc.d/init.d/livesys-late' lacks a native systemd unit file.
Automatically generating a unit file for compatibility. Please update
package to include a native systemd unit file, in order to make it
more safe and robust.
[  366.970723] uvcvideo: Failed to query (SET_CUR) UVC control 10 on
unit 2: -32 (exp. 2).
[  366.987741] uvcvideo: Failed to query (SET_CUR) UVC control 4 on
unit 1: -32 (exp. 4).
---------------------------

Paul

[Jonathan Billings]

On Thu, Apr 29, 2021 at 02:17:50PM +0100, Paul Smith wrote:
> The answers to all your questions is YES, but 'dmesg' returns the following:
>
> [  263.923694] EDAC amd64: Node 0: DRAM ECC disabled.
> [  265.686950] systemd-sysv-generator[37295]: SysV service
> '/etc/rc.d/init.d/livesys' lacks a native systemd unit file.
> Automatically generating a unit file for compatibility. Please update
> package to include a native systemd unit file, in order to make it
> more safe and robust.
> [  265.686995] systemd-sysv-generator[37295]: SysV service
> '/etc/rc.d/init.d/livesys-late' lacks a native systemd unit file.
> Automatically generating a unit file for compatibility. Please update
> package to include a native systemd unit file, in order to make it
> more safe and robust.
> [  366.970723] uvcvideo: Failed to query (SET_CUR) UVC control 10 on
> unit 2: -32 (exp. 2).
> [  366.987741] uvcvideo: Failed to query (SET_CUR) UVC control 4 on
> unit 1: -32 (exp. 4).

I don't see anything in particular wrong with that.  The uvcvideo
output is probably for your real video device.

Do you see the v4l2loopback device in v4l2-ctrl?  For example, I
loaded the rpmfusion package 'akmod-v4l2loopback' and enabled the
akmods service, and now I see:

$ v4l2-ctl --list-devices
OBS Virtual Camera (platform:v4l2loopback-000):
    /dev/video0

[Paul Smith]

On Thu, Apr 29, 2021 at 3:59 PM Jonathan Billings  wrote:
> > [  263.923694] EDAC amd64: Node 0: DRAM ECC disabled.
> > [  265.686950] systemd-sysv-generator[37295]: SysV service
> > '/etc/rc.d/init.d/livesys' lacks a native systemd unit file.
> > Automatically generating a unit file for compatibility. Please update
> > package to include a native systemd unit file, in order to make it
> > more safe and robust.
> > [  265.686995] systemd-sysv-generator[37295]: SysV service
> > '/etc/rc.d/init.d/livesys-late' lacks a native systemd unit file.
> > Automatically generating a unit file for compatibility. Please update
> > package to include a native systemd unit file, in order to make it
> > more safe and robust.
> > [  366.970723] uvcvideo: Failed to query (SET_CUR) UVC control 10 on
> > unit 2: -32 (exp. 2).
> > [  366.987741] uvcvideo: Failed to query (SET_CUR) UVC control 4 on
> > unit 1: -32 (exp. 4).
>
> I don't see anything in particular wrong with that.  The uvcvideo
> output is probably for your real video device.
>
> Do you see the v4l2loopback device in v4l2-ctrl?  For example, I
> loaded the rpmfusion package 'akmod-v4l2loopback' and enabled the
> akmods service, and now I see:
>
> $ v4l2-ctl --list-devices
> OBS Virtual Camera (platform:v4l2loopback-000):
>         /dev/video0

Thanks, Jonathan. In my case, I get:

$ v4l2-ctl --list-devices
OBS Virtual Camera (platform:v4l2loopback-000):
    /dev/video0

EasyCamera 5M: EasyCamera 5M (usb-0000:01:00.0-7):
    /dev/video2
    /dev/video3
$

Paul

[Paul Smith]

On Thu, Apr 29, 2021 at 4:12 PM Paul Smith  wrote:
> On Thu, Apr 29, 2021 at 3:59 PM Jonathan Billings  wrote:
> > > [  263.923694] EDAC amd64: Node 0: DRAM ECC disabled.
> > > [  265.686950] systemd-sysv-generator[37295]: SysV service
> > > '/etc/rc.d/init.d/livesys' lacks a native systemd unit file.
> > > Automatically generating a unit file for compatibility. Please update
> > > package to include a native systemd unit file, in order to make it
> > > more safe and robust.
> > > [  265.686995] systemd-sysv-generator[37295]: SysV service
> > > '/etc/rc.d/init.d/livesys-late' lacks a native systemd unit file.
> > > Automatically generating a unit file for compatibility. Please update
> > > package to include a native systemd unit file, in order to make it
> > > more safe and robust.
> > > [  366.970723] uvcvideo: Failed to query (SET_CUR) UVC control 10 on
> > > unit 2: -32 (exp. 2).
> > > [  366.987741] uvcvideo: Failed to query (SET_CUR) UVC control 4 on
> > > unit 1: -32 (exp. 4).
> >
> > I don't see anything in particular wrong with that.  The uvcvideo
> > output is probably for your real video device.
> >
> > Do you see the v4l2loopback device in v4l2-ctrl?  For example, I
> > loaded the rpmfusion package 'akmod-v4l2loopback' and enabled the
> > akmods service, and now I see:
> >
> > $ v4l2-ctl --list-devices
> > OBS Virtual Camera (platform:v4l2loopback-000):
> >         /dev/video0
>
> Thanks, Jonathan. In my case, I get:
>
> $ v4l2-ctl --list-devices
> OBS Virtual Camera (platform:v4l2loopback-000):
>     /dev/video0
>
> EasyCamera 5M: EasyCamera 5M (usb-0000:01:00.0-7):
>     /dev/video2
>     /dev/video3
> $

This may be related:

------------------------------
$ ffmpeg -i /dev/video2 -f v4l2 /dev/video4
ffmpeg version 4.4 Copyright (c) 2000-2021 the FFmpeg developers
  built with gcc 11 (GCC)
  configuration: --prefix=/usr --bindir=/usr/bin
--datadir=/usr/share/ffmpeg --docdir=/usr/share/doc/ffmpeg
--incdir=/usr/include/ffmpeg --libdir=/usr/lib64
--mandir=/usr/share/man --arch=x86_64 --optflags='-O2 -flto=auto
-ffat-lto-objects -fexceptions -g -grecord-gcc-switches -pipe -Wall
-Werror=format-security -Wp,-D_FORTIFY_SOURCE=2
-Wp,-D_GLIBCXX_ASSERTIONS
-specs=/usr/lib/rpm/redhat/redhat-hardened-cc1
-fstack-protector-strong -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1
-m64 -mtune=generic -fasynchronous-unwind-tables
-fstack-clash-protection -fcf-protection'
--extra-ldflags='-Wl,-z,relro -Wl,--as-needed -Wl,-z,now
-specs=/usr/lib/rpm/redhat/redhat-hardened-ld ' --extra-cflags='
-I/usr/include/rav1e' --enable-libopencore-amrnb
--enable-libopencore-amrwb --enable-libvo-amrwbenc --enable-version3
--enable-bzlib --disable-crystalhd --enable-fontconfig --enable-frei0r
--enable-gcrypt --enable-gnutls --enable-ladspa --enable-libaom
--enable-libdav1d --enable-libass --enable-libbluray --enable-libcdio
--enable-libdrm --enable-libjack --enable-libfreetype
--enable-libfribidi --enable-libgsm --enable-libmp3lame
--enable-libmysofa --enable-nvenc --enable-openal --enable-opencl
--enable-opengl --enable-libopenjpeg --enable-libopenmpt
--enable-libopus --enable-libpulse --enable-librsvg --enable-librav1e
--enable-libsmbclient --enable-version3 --enable-libsoxr
--enable-libspeex --enable-libsrt --enable-libssh --enable-libsvtav1
--enable-libtheora --enable-libvorbis --enable-libv4l2
--enable-libvidstab --enable-libvmaf --enable-version3
--enable-vapoursynth --enable-libvpx --enable-vulkan
--enable-libglslang --enable-libx264 --enable-libx265 --enable-libxvid
--enable-libxml2 --enable-libzimg --enable-libzvbi --enable-lv2
--enable-avfilter --enable-avresample --enable-libmodplug
--enable-postproc --enable-pthreads --disable-static --enable-shared
--enable-gpl --disable-debug --disable-stripping --shlibdir=/usr/lib64
--enable-lto --enable-libmfx --enable-runtime-cpudetect
  libavutil      56. 70.100 / 56. 70.100
  libavcodec     58.134.100 / 58.134.100
  libavformat    58. 76.100 / 58. 76.100
  libavdevice    58. 13.100 / 58. 13.100
  libavfilter     7.110.100 /  7.110.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  9.100 /  5.  9.100
  libswresample   3.  9.100 /  3.  9.100
  libpostproc    55.  9.100 / 55.  9.100
Input #0, video4linux2,v4l2, from '/dev/video2':
  Duration: N/A, start: 7710.349826, bitrate: 110592 kb/s
  Stream #0:0: Video: rawvideo (YUY2 / 0x32595559), yuyv422, 640x360,
110592 kb/s, 30 fps, 30 tbr, 1000k tbn, 1000k tbc
Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo (native) -> rawvideo (native))
Press [q] to stop, [?] for help
[video4linux2,v4l2 @ 0x55c856f6b040] Unable to open V4L2 device '/dev/video4'
Could not write header for output file #0 (incorrect codec parameters
?): No such file or directory
Error initializing output stream 0:0 --
Conversion failed!
$
------------------------------

Paul

[Paul Smith]

Solved! I will later describe the solution I found for my problem, as
I am now in a hurry.

Paul

On Thu, Apr 29, 2021 at 4:18 PM Paul Smith  wrote:
> On Thu, Apr 29, 2021 at 4:12 PM Paul Smith  wrote:
> > On Thu, Apr 29, 2021 at 3:59 PM Jonathan Billings  wrote:
> > > > [  263.923694] EDAC amd64: Node 0: DRAM ECC disabled.
> > > > [  265.686950] systemd-sysv-generator[37295]: SysV service
> > > > '/etc/rc.d/init.d/livesys' lacks a native systemd unit file.
> > > > Automatically generating a unit file for compatibility. Please update
> > > > package to include a native systemd unit file, in order to make it
> > > > more safe and robust.
> > > > [  265.686995] systemd-sysv-generator[37295]: SysV service
> > > > '/etc/rc.d/init.d/livesys-late' lacks a native systemd unit file.
> > > > Automatically generating a unit file for compatibility. Please update
> > > > package to include a native systemd unit file, in order to make it
> > > > more safe and robust.
> > > > [  366.970723] uvcvideo: Failed to query (SET_CUR) UVC control 10 on
> > > > unit 2: -32 (exp. 2).
> > > > [  366.987741] uvcvideo: Failed to query (SET_CUR) UVC control 4 on
> > > > unit 1: -32 (exp. 4).
> > >
> > > I don't see anything in particular wrong with that.  The uvcvideo
> > > output is probably for your real video device.
> > >
> > > Do you see the v4l2loopback device in v4l2-ctrl?  For example, I
> > > loaded the rpmfusion package 'akmod-v4l2loopback' and enabled the
> > > akmods service, and now I see:
> > >
> > > $ v4l2-ctl --list-devices
> > > OBS Virtual Camera (platform:v4l2loopback-000):
> > >         /dev/video0
> >
> > Thanks, Jonathan. In my case, I get:
> >
> > $ v4l2-ctl --list-devices
> > OBS Virtual Camera (platform:v4l2loopback-000):
> >     /dev/video0
> >
> > EasyCamera 5M: EasyCamera 5M (usb-0000:01:00.0-7):
> >     /dev/video2
> >     /dev/video3
> > $
>
> This may be related:
>
> $ ffmpeg -i /dev/video2 -f v4l2 /dev/video4
> ffmpeg version 4.4 Copyright (c) 2000-2021 the FFmpeg developers
>   built with gcc 11 (GCC)
>   configuration: --prefix=/usr --bindir=/usr/bin
> --datadir=/usr/share/ffmpeg --docdir=/usr/share/doc/ffmpeg
> --incdir=/usr/include/ffmpeg --libdir=/usr/lib64
> --mandir=/usr/share/man --arch=x86_64 --optflags='-O2 -flto=auto
> -ffat-lto-objects -fexceptions -g -grecord-gcc-switches -pipe -Wall
> -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2
> -Wp,-D_GLIBCXX_ASSERTIONS
> -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1
> -fstack-protector-strong -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1
> -m64 -mtune=generic -fasynchronous-unwind-tables
> -fstack-clash-protection -fcf-protection'
> --extra-ldflags='-Wl,-z,relro -Wl,--as-needed -Wl,-z,now
> -specs=/usr/lib/rpm/redhat/redhat-hardened-ld ' --extra-cflags='
> -I/usr/include/rav1e' --enable-libopencore-amrnb
> --enable-libopencore-amrwb --enable-libvo-amrwbenc --enable-version3
> --enable-bzlib --disable-crystalhd --enable-fontconfig --enable-frei0r
> --enable-gcrypt --enable-gnutls --enable-ladspa --enable-libaom
> --enable-libdav1d --enable-libass --enable-libbluray --enable-libcdio
> --enable-libdrm --enable-libjack --enable-libfreetype
> --enable-libfribidi --enable-libgsm --enable-libmp3lame
> --enable-libmysofa --enable-nvenc --enable-openal --enable-opencl
> --enable-opengl --enable-libopenjpeg --enable-libopenmpt
> --enable-libopus --enable-libpulse --enable-librsvg --enable-librav1e
> --enable-libsmbclient --enable-version3 --enable-libsoxr
> --enable-libspeex --enable-libsrt --enable-libssh --enable-libsvtav1
> --enable-libtheora --enable-libvorbis --enable-libv4l2
> --enable-libvidstab --enable-libvmaf --enable-version3
> --enable-vapoursynth --enable-libvpx --enable-vulkan
> --enable-libglslang --enable-libx264 --enable-libx265 --enable-libxvid
> --enable-libxml2 --enable-libzimg --enable-libzvbi --enable-lv2
> --enable-avfilter --enable-avresample --enable-libmodplug
> --enable-postproc --enable-pthreads --disable-static --enable-shared
> --enable-gpl --disable-debug --disable-stripping --shlibdir=/usr/lib64
> --enable-lto --enable-libmfx --enable-runtime-cpudetect
>   libavutil      56. 70.100 / 56. 70.100
>   libavcodec     58.134.100 / 58.134.100
>   libavformat    58. 76.100 / 58. 76.100
>   libavdevice    58. 13.100 / 58. 13.100
>   libavfilter     7.110.100 /  7.110.100
>   libavresample   4.  0.  0 /  4.  0.  0
>   libswscale      5.  9.100 /  5.  9.100
>   libswresample   3.  9.100 /  3.  9.100
>   libpostproc    55.  9.100 / 55.  9.100
> Input #0, video4linux2,v4l2, from '/dev/video2':
>   Duration: N/A, start: 7710.349826, bitrate: 110592 kb/s
>   Stream #0:0: Video: rawvideo (YUY2 / 0x32595559), yuyv422, 640x360,
> 110592 kb/s, 30 fps, 30 tbr, 1000k tbn, 1000k tbc
> Stream mapping:
>   Stream #0:0 -> #0:0 (rawvideo (native) -> rawvideo (native))
> Press [q] to stop, [?] for help
> [video4linux2,v4l2 @ 0x55c856f6b040] Unable to open V4L2 device '/dev/video4'
> Could not write header for output file #0 (incorrect codec parameters
> ?): No such file or directory
> Error initializing output stream 0:0 --
> Conversion failed!
> $
>
> Paul

[Paul Smith]

On Thu, Apr 29, 2021 at 4:28 PM Paul Smith  wrote:
> Solved! I will later describe the solution I found for my problem, as
> I am now in a hurry.

The problem appears to be related to OBS-Studio. After having run the
following command, the reported problem disappeared:

ffmpeg -i /dev/video1 -f v4l2 /dev/video0

Therefore, I suspect that OBS-Studio does not issue a command like the
above -- one has to do that manually.

Paul