Error: v4l2loopback does not work

[hissssst]

Description

wf-recorder started with specific options (as described in #43) should record screen output to /dev/video2

Steps to reproduce

1. Install required dependencies (which are described in #43)
2. Check loopback with $ v4l2-ctl --list-devices
3. Run wf-recorder

   $ wf-recorder --muxer=v4l2 --codec=rawvideo --file=/dev/video2
   selected region 0 0 0 0
   Choosing pixel format bgr0
   Output #0, video4linux2,v4l2, to '/dev/video2':
   Stream #0:0: Unknown: none (rawvideo)
   [video4linux2,v4l2 @ 0x7ff998000d00] Using AVStream.codec to pass codec parameters to muxers is deprecated, use AVStream.codecpar instead.

4. Check video on /dev/video2

   $ cat /dev/video2 | pv
   0.00 B 0:00:03 [0.00 B/s] [<=>

   Even ffplay /dev/video2 shows nothing

[soreau]

The wiki says to use -x yuv420p. Are you doing this?

[hissssst]

43 sais this option is optional. Anyway, it doesn't work with this option either. I am ready to provide some debug and versions info, just tell me which ones

[soreau]

You might need to install the latest version of the v4l2loopback module.

[hissssst]

I have v4l2loopback installed and probed. v4l2-ctl shows /dev/video2

[hissssst]

@ammen99 ping

[ammen99]

@hissssst I do not know how to help you. As far as I know, v4l2loopback works on my machine, and on many others, so this could be just a problem in your setup.

The only difference between your command and mine is that I am running with wf-recorder --muxer=v4l2 --codec=rawvideo --pixel-format=yuv420p --file=/dev/video2 (note the pixel format option).

[hissssst]

@ammen99 Ok, I won't close this issue just in case if someone experienced with v4l2 comes by... I am ready to provide all diagnostic info and stuff

[soreau]

To reiterate, if you haven't already, my suggestion is to build latest v4l2loopback module from git and load the .ko with insmod. You don't have to install it globally. I can say this fixed the situation at least once for me in the past.

[roosemberth]

I got v4l2loopback working with the following command: wf-recorder --muxer=v4l2 -f /dev/video4 -c rawvideo -x yuyv422. I just need to figure how to mirror (or rather unmirror) the image :( (edit: image is not mirrored in the other side.)

[WhyNotHugo]

I was having the same error as op:

$ wf-recorder --muxer=v4l2 -f /dev/video2 -c rawvideo -x yuyv422
Output file "/dev/video2" exists. Overwrite? Y/n: y
Please select an output from the list to capture (enter output no.):
1. Name: eDP-1 Description: Chimei Innolux Corporation 0x14D4 0x00000000 (eDP-1)
2. Name: HDMI-A-2 Description: Ancor Communications Inc ROG PG348Q K8LMQS109773 (HDMI-A-2)
Enter output no.:1
selected region 0 0 0 0
Choosing pixel format yuyv422
Output #0, video4linux2,v4l2, to '/dev/video2':
    Stream #0:0: Unknown: none (rawvideo)
[video4linux2,v4l2 @ 0x7f320c000d00] Using AVStream.codec to pass codec parameters to muxers is deprecated, use AVStream.codecpar instead.
[video4linux2,v4l2 @ 0x7f320c000d00] ioctl(VIDIOC_G_FMT): Invalid argument
Failed to write file header
Invalid argument

I got v4l2loopback working with the following command: wf-recorder --muxer=v4l2 -f /dev/video4 -c rawvideo -x yuyv422

This works for me. Turns out I was pointing to /dev/video2, but that was the actual webcam. Not sure what /dev/video3 is, but video4 is the v4l2loopback one.

@hissssst Can you check what /dev/video* devices you have?

[hissssst]

@WhyNotHugo I have /dev/video0 and /dev/video1 /dev/video0 is my webcam while /dev/video1 shows

$ mpv /dev/video1
[ffmpeg/demuxer] video4linux2,v4l2: ioctl(VIDIOC_G_INPUT): Inappropriate ioctl for device
[lavf] avformat_open_input() failed
[ffmpeg/demuxer] video4linux2,v4l2: ioctl(VIDIOC_G_INPUT): Inappropriate ioctl for device
[lavf] avformat_open_input() failed
Failed to recognize file format.

Exiting... (Errors when loading file)

I've tried starting wf-recorder at /dev/video1 and it fails as you've described in your comment. And at /dev/video2

$ wf-recorder --muxer=v4l2 -f /dev/video2 -c rawvideo -x yuyv422
selected region 0 0 0 0
Choosing pixel format yuyv422
Output #0, video4linux2,v4l2, to '/dev/video2':
    Stream #0:0: Unknown: none (rawvideo)
avio_open failed

[Figuera]

Although the recording work for me, meaning that I can watch it using ffplay. I can't use it as a webcam in Zoom, it shows as blank. I am using --pixel-format=yuv420p. Anything else I could try? Maybe some debuging tests.

[telamon]

Hey! So let me just say thanks to everyone for the info above, I got the playback successfully working in VLC though I would like to be able to share my screen via electron apps (at least as a dummy-webcam) for work.

So I did some digging and from what I can tell from discord's log-output the main complaint is:

[299:264] [97] (webrtcvideocapturer.cc:179): Failed to find usable formats for id: platform:v4l2loopback-000

Tracing that to chromium source I can see that it's trying to enumerate the capabilities of the loop-back device in an attempt to discover what format the stream is available in.

So i turned to the utility v4l2loopback-ctl that came with the dkms module, it has this nifty hack to force set capabilities for a stream that I hoped would be picked up by electron's enumerator.

v4l2loopback-ctl set-caps "video/x-raw, format=YUY2, width=2560, height=1440" /dev/video4

Sadly I did not get the expected results, discord still shows the log-line and a black screen. Here's my "workspace" script in case anyone could help me me solve the issue: sharescreen.sh

[hissssst]

Over the years, I am not experiencing the problem anymore, since it got fixed and I've missed it somehow. Thanks, @ammen99