[gst-devel] 2x2 videowall pipeline

[David Balch]

Hi,

I'm trying to combine four v4l2 webcam streams into one, and earlier
mails on the list* have been invaluable to my progress so far - my
thanks to the list!

I've managed to combine four test signals successfully with this:

gst-launch-0.10 videotestsrc pattern="snow" !
video/x-raw-yuv,width=320,height=240 ! queue ! videomixer name=mix !
ffmpegcolorspace ! autovideosink \
  videotestsrc pattern="red" ! video/x-raw-yuv,width=320,height=240 !
videobox left=-320 border-alpha=0  ! queue ! mix. \
  videotestsrc pattern="green" ! video/x-raw-yuv,width=320,height=240
! videobox top=-240 border-alpha=0 ! queue ! mix. \
  videotestsrc pattern="blue" ! video/x-raw-yuv,width=320,height=240 !
videobox left=-320 top=-240 border-alpha=0 ! queue ! mix.


Directly switching out a videotestsrc for a v4l2src gives "ERROR: from
element /GstPipeline:pipeline0/GstV4l2Src:v4l2src0: Internal data flow
error. ", so with a bit of ffmpegcolorspace experimentation I can make
a pipeline that runs without error:

gst-launch-0.10 v4l2src device=/dev/video0 !
video/x-raw-yuv,width=320,height=240 ! queue ! videomixer name=mix !
ffmpegcolorspace ! autovideosink \
  videotestsrc pattern="green" ! video/x-raw-yuv,width=320,height=240
! videobox left=-320 border-alpha=0 ! ffmpegcolorspace ! queue ! mix.
\
  videotestsrc pattern="blue" ! video/x-raw-yuv,width=320,height=240 !
videobox top=-240 border-alpha=0 ! ffmpegcolorspace ! queue ! mix. \
  videotestsrc pattern="red" ! video/x-raw-yuv,width=320,height=240 !
videobox left=-320 top=-240 border-alpha=0 ! ffmpegcolorspace ! queue
! mix.

Unfortunately, the webcam doesn't actually show - it's corner is just
black. (The webcam works with "gst-launch-0.10 v4l2src
device=/dev/video0 ! video/x-raw-yuv,width=320,height=240 !
autovideosink".)


Any ideas why the webcam doesn't appear, and how to fix it?

Cheers,
Dave.

*e.g. http://gstreamer-devel.966125.n4.nabble.com/Videomixing-two-multiple-webcams-side-by-side-td2197804.html

-- 
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