[PD] Gem+v4l2loopback (was Re: pdp_vloopback ?)

Mario Mey mariomey at gmail.com
Thu Apr 23 15:51:01 CEST 2015

Well, I don't know if I was on 'video' group but I did the addition.  I 
checked the file you sent me and it works. However, for the moment, I 
have 3 questions:

- If I don't activate the device in the right side of the patch, nor 
Blender nor VLC can get the image from /dev/video1 (VLC shows errors on 
console, Blender says nothing, but it makes black texture) Why is like 
that? Supposedly, being pix_record there and activated, I should get 
from where I want...

- Look at the attached image: why the video is vertically inverted? I 
don't know about GEM, but I didn't find any object that do that.

- How the patch should be if I want to send the GEM window to loopback? 
I mean, not only the color and vertical inverted video, but the whole 

Thank you very much!

El 22/04/15 a las 11:14, Antoine Villeret escibió:
> Hi,
> the Iohannes' instructions are still relevant but there are few things 
> you might pay attention to :
> - be sure you belong to "video" group, if you got an error like 
> "[pix_record] : can't open /dev/video1" this could be the issue (if 
> /dev/video1 exists of course)
> - set and start the capture *before* setting the device capture. The 
> v4l2device is undefined (nor a capture or a tuner device) until you 
> send the first frame to it.
> here is attached a sample patch that works with current Gem from git.
> best
> antoine
> Le mer. 22 avr. 2015 à 15:06, Mario Mey <mariomey at gmail.com 
> <mailto:mariomey at gmail.com>> a écrit :
>     Hi, there. I'm reviving a mail from 2011... here it is the last of
>     the thread:
>     http://lists.puredata.info/pipermail/pd-list/2011-02/086741.html
>     I was looking for help to use Gem with v4l2loopback.
>     These mails are the only ones where I found the way to do
>     it (no other place in internet).
>     After installing v4l2loopback kernel module, I did what IOhannes said:
>     ------------
>     you should be able to use [pix_record] with v4l2loopback.
>     just do:
>     - - create [pix_record]
>     - - check at the console whether it prints something like
>     "[pix_record]:
>     backend #1='V4L2'" (this will only happen the first time you create a
>     [pix_record] object for hygienic reasons)
>     - - if so, continue
>     - - set the codec to "v4l2" and the output filename to /dev/video1 (or
>     whatever your loopback-device is).
>     something like [codec v4l2, filename /dev/video1, record 1( should do
>     the trick.
>     f
>     gmasdr
>     IOhannes
>     -----------
>     Now, there is /dev/video1 (also, /dev/video0 from Webcam). But, when
>     I try to open that device with VLC, I got this error:
>     [0x7fed08000e28] v4l2 demux error: not a video capture device
>     [0x7fed08000e28] v4l2 demux error: not a radio tuner device
>     [0x7fed08000e08] v4l2 access error: not a video capture device
>     [0x7fed18003898] main input error: open of `v4l2:///dev/video1' failed
>     I tried to open with Blender, videoOnTexture, but the texture
>     is black. There's no error messages.
>     What am I doing wrong?
>     I have Pd-extended 0.44.0-extended-20130808, Ubuntu 14.04.
>     I don't know how to know Gem version.
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