Failed to open /dev/video0: No such file or directory

Question

I have been trying to setup my DSLR to be a webcam with the following command: gphoto2 --stdout --capture-movie | ffmpeg -i - -vcodec rawvideo -threads 0 -f v4l2 /dev/video0 this however results in the following error:

hutber@hutber:~/v4l2loopback-master$ gphoto2 --stdout --capture-movie | ffmpeg -i - -vcodec rawvideo -threads 0 -f v4l2 /dev/video4
ffmpeg version N-49161-g50e194e6e1-static https://johnvansickle.com/ffmpeg/  Copyright (c) 2000-2019 the FFmpeg developers
  built with gcc 6.3.0 (Debian 6.3.0-18+deb9u1) 20170516
  configuration: --enable-gpl --enable-version3 --enable-static --disable-debug --disable-ffplay --disable-indev=sndio --disable-outdev=sndio --cc=gcc-6 --enable-fontconfig --enable-frei0r --enable-gnutls --enable-gmp --enable-gray --enable-libaom --enable-libfribidi --enable-libass --enable-libvmaf --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librubberband --enable-libsoxr --enable-libspeex --enable-libsrt --enable-libvorbis --enable-libopus --enable-libtheora --enable-libvidstab --enable-libvo-amrwbenc --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libdav1d --enable-libxvid --enable-libzvbi --enable-libzimg
  libavutil      56. 30.100 / 56. 30.100
  libavcodec     58. 53.101 / 58. 53.101
  libavformat    58. 28.101 / 58. 28.101
  libavdevice    58.  7.100 / 58.  7.100
  libavfilter     7. 55.100 /  7. 55.100
  libswscale      5.  4.101 /  5.  4.101
  libswresample   3.  4.100 /  3.  4.100
  libpostproc    55.  4.100 / 55.  4.100
Capturing preview frames as movie to 'stdout'. Press Ctrl-C to abort.
[mjpeg @ 0x6d04900] Format mjpeg detected only with low score of 25, misdetection possible!
Input #0, mjpeg, from 'pipe:':
  Duration: N/A, bitrate: N/A
    Stream #0:0: Video: mjpeg (Baseline), yuvj422p(pc, bt470bg/unknown/unknown), 640x426, 25 tbr, 1200k tbn, 25 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (mjpeg (native) -> rawvideo (native))
[video4linux2,v4l2 @ 0x6d07d00] 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!

However this errors to create the dummy device, that at the same time is not accessible

hutber@hutber:~/v4l2loopback-master$ v4l2-ctl --list-devices
Dummy video device (0x0000) (platform:v4l2loopback-000):
    /dev/video2

Failed to open /dev/video0: No such file or directory

I would like the /dev/video0 to be available to use as a webcam and believe the issue lies somewhere in the v412.

[Edit]

After restarting the machine I now see:

hutber@hutber:~$ v4l2-ctl --list-devices
Failed to open /dev/video0: No such file or directory

It says there is a Dummy Video Device, but I cannot see any devices when trying to use the dummy video.

Solution

Unable to open V4L2 device '/dev/video0'

or

Failed to open /dev/video0: No such file or directory

Two potential problems:

• Wrong video number. The number can change depending on the number of existing webcams. Check output of ls /dev/video* or v4l2-ctl --list-devices.
• v4l2loopback module is not enabled or installed. If you already installed v4l2loopback run sudo modprobe v4l2loopback. Then check output of ls /dev/video* or v4l2-ctl --list-devices. If you did not yet install it see Is there any way ffmpeg send video to /dev/video0 on Ubuntu?.

Unknown V4L2 pixel format equivalent for yuvj422p

The V4L2 output device only supported a limited number of pixel formats. Add the format filter to your command to give it a compatible pixel format:

gphoto2 --stdout --capture-movie | ffmpeg -i - -vf format=yuv420p -f v4l2 /dev/video0

Comments

[llogan]

Run sudo modprobe v4l2loopback as shown in Is there any way ffmpeg send video to /dev/video0 on Ubuntu? and then show output from v4l2-ctl --list-devices.

[Jamie Hutber]

Thanks Llogan, I see you're helping on both quesitons. Thank you. I have updated with a screenshot.

[Jamie Hutber]

If I reset my machine, then the Dummy video device will no longer be there, but I will still experience the same errors when trying to pipe through to ffmpeg

[llogan]

Now try gphoto2 --stdout --capture-movie | ffmpeg -i - -c:v rawvideo -f v4l2 /dev/video0

[Jamie Hutber]

Thanks again, new error: [video4linux2,v4l2 @ 0x589f700] Unknown V4L2 pixel format equivalent for yuvj422p

[Raffa]

Does this answer your question? Use webcam from laptop on desktop pc

[Jamie Hutber]

I think the step that I was missing is sudo modprobe v412loopback llogan. With a refresh restart. Thank you again