v4l2loopback and gstreamer

[giorgino]

Hi All I need your support in order to solve an issue. I had a usb camera that has to be used at the same time by two different application. This it is obviously a problem because when I launch the second application, system says me that the resource is busy. I thought that the solution can be to install v4l2loopback and execute it. In this way I have two devices that are
/dev/video0 and /dev/video1. So I launched

gst-launch v4l2src device=/dev/video0 ! autovideosink

and after
 
gst-launch v4l2src device=/dev/video1 ! autovideosink

The first pipe works well but the second one goes on error with the following message

Impostazione della pipeline a PAUSED ...
libv4l2: error getting pixformat: Argomento non valido
ERRORE: la pipeline non vuole mettersi in pausa.
ERRORE: dall'elemento /GstPipeline:pipeline0/GstV4l2Src:v4l2src0: Could not negotiate format
Informazioni di debug aggiuntive:
gstbasesrc.c(2755): gst_base_src_start (): /GstPipeline:pipeline0/GstV4l2Src:v4l2src0:
Check your filtered caps, if any
Impostazione della pipeline a NULL ...
Esecuzione di free sulla pipeline...


How I can solve this issue?

[Stefan Sauer]

Am 28.01.2011 16:16, schrieb giorgino:

>
> Hi All I need your support in order to solve an issue. I had a usb camera
> that has to be used at the same time by two different application. This it
> is obviously a problem because when I launch the second application, system
> says me that the resource is busy. I thought that the solution can be to
> install v4l2loopback and execute it. In this way I have two devices that are
> /dev/video0 and /dev/video1. So I launched
>
> gst-launch v4l2src device=/dev/video0 ! autovideosink
>
> and after
>  
> gst-launch v4l2src device=/dev/video1 ! autovideosink
>
> The first pipe works well but the second one goes on error with the
> following message
>
> Impostazione della pipeline a PAUSED ...
> libv4l2: error getting pixformat: Argomento non valido
> ERRORE: la pipeline non vuole mettersi in pausa.
> ERRORE: dall'elemento /GstPipeline:pipeline0/GstV4l2Src:v4l2src0: Could not
> negotiate format
> Informazioni di debug aggiuntive:
> gstbasesrc.c(2755): gst_base_src_start ():
> /GstPipeline:pipeline0/GstV4l2Src:v4l2src0:
> Check your filtered caps, if any
> Impostazione della pipeline a NULL ...
> Esecuzione di free sulla pipeline...
>
>
> How I can solve this issue?
>

Please file a bug and attatch:
- information of how to setup the v4l2loopback device
- a (compressed) log for the 2nd GST_DEBUG="':5" gst-launch 2>debug.log v4l2src
device=/dev/video1 ! autovideosink

Stefan

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[giorgino]

Hi and thanks for the answer.
using the following pipe
gst-launch -v v4l2src  ! v4l2sink device=/dev/video1

and in another terminal

gst-launch v4l2src device=/dev/video1 ! autovideosink

it works although the quality is poor. But if I try to launch the second pipe as an application in another language (python, java) I don't see the video because I think the v4l2loopback driver had some limitations.
I tried other ways without solve the isse. I repeat my issue is that to be able to use only a webcam and capture it from two different applications. Do you have any ideas? (I tried with udpsink, filesink, symbolic link, fifo  without any success)

G.