I think the most painful thing about this endeavor is that I will eventually find the solutions to my problems and write them up here, but because I'm just some weird toy-therian thing on the Internet, many others with the same problems will not get to read about it.

Good documentation is invaluable and simply not available here.

There are so many examples of things someone might want to do, but none of them are what I want to do, and the essential information I'd need to figure that out for myself is not here. I don't know what option I should use in ffmpeg to get v4l2 to pass the right codec, resolution, and framerate info to my webcam. I don't know where I'd find that written up anywhere.

I can't be expected to read the manual if it's not there.

Is there complete documentation of v4l2-ctl anywhere? Because the man page I got with the package isn't it.

I saw the --list-formats-ext option recommended to list all the available formats for a device, which works, but isn't documented. I'm guessing that I need a corresponding option to set the format I want, but I have no idea because the documentation isn't there.

#V4L2 #Video4Linux #WhereIsTheManual

Am I even supposed to be using v4l2-ctl to change the stream format for other applications?

I have no idea! None of this is documented! There's no one to tell me!

Was I able to find documentation of the commands? Yes, doing v4l2-ctl --help-vidcap, which is documented in the man page. That probably should have just been another man page.

Was I able to change the pixelformat on my camera to MJPG? Yes, by doing v4l2-ctl -d /dev/video0 --set-fmt-video=pixelformat=MJPG.

Does this make a difference when I do mpv /dev/video0 to check the video output? Nope! It gets set back to YUYV raw video at 5fps.

So I do actually need to figure out how to set the correct format in ffmpeg or whatever I use to stream to the loopback device?

#V4L2 #Video4Linux #V4L2loopack #WhereIsTheManual

I've reached the point with ffmpeg where I really need someone to explain something to me because I'm getting inconsistent results.

To get ffplay to show me the video I want to stream to my v4l2loopback device, I did this:

And it worked! It pops up a window showing video from my webcam at the correct resolution and framerate, in MJPEG as expected.

But when I do this:

The stream goes back to raw video at 5fps.

Is there something wrong with my syntax? I've noticed that if I move -i /dev/video0 anywhere except as the first argument in the command, I get errors. For example I do:

And the error I get is:

#V4L2 #Video4Linux #v4l2loopback #ffmpeg

Solution to my ffmpeg issue!

Thank you so much woggle from FurNet.

The command I ran was:

I don't know why the arguments need to be in this order, but it gave me the streamcopy I needed.

Well, it gave me one streamcopy. Turns out that only one application can access a virtual webcam, same as only one application can access a physical webcam. So next step is to make more loopback devices and streamcopy to all of them.

#V4L2 #Video4Linux #v4l2loopback #ffmpeg