gst-launch + alpha

[Alain Culos]

On Wed, 8 Apr 2020, at 18:14, Alain Culos wrote:
> Thank you both Ederson & Arnaud,
> 
> This pipeline now works without error messages:
> 
> w=1280; h=800; x0=450; y0=200; gst-launch-1.0
>     v4l2src device=/dev/video0 \
>     ! videocrop left=$x0 right=$(( 1920 - $w - $x0 )) top=$y0 
> bottom=$(( 1080 - $h - $y0 )) \
>     ! alpha method=green angle=70 \
>     ! queue \
>     ! mixer.sink_1 \
>     \
>     ximagesrc xid=0x06600003 use-damage=false \
>     ! videoscale \
>     ! video/x-raw,width=$w,height=$h \
>     ! queue \
>     ! mixer.sink_0 \
>     \
>     videomixer name=mixer sink_0::zorder=0 sink_1::zorder=1 \
>     ! videoconvert \
>     ! autovideosink -v sync=false
> 
> The time-lag is significant and the displayed framerate is poor (maybe 
> 5/1 to 10/1), but it works.
> Note that my desktop hardly works at all (overall CPU well below 10%, 1 
> of 12 cores at 10-20% max).
> 
> 1/ It would be great if someone could chime in with ideas to help 
> improve the real-time performance of this pipeline - ideally resulting 
> in a framerate of at least 15 or 20.
> 
> 2/ My next step is to use the "alpha" element properly.
> With the pipeline above my green screen gets replaced with a shaded 
> background - i.e. alpha is not 0 or 1, but something in between.
> How do I increase the alpha channel values?
I said something wrong about becoming transparent. I pushed the angle to 90, and the alpha channel still isn't 100% transparent. I am fine though.

> Thanks,
> Alain.
> 
> 
> On Wed, 8 Apr 2020, at 13:27, Arnaud Loonstra wrote:
> > On 08-04-2020 12:38, Alain Culos wrote:
> > [big snip]
> > 
> > I tried your pipeline but couldn't get it to work. I think it'll run a 
> > lot smoother by adding sync=false to your imagesink.
> > 
> > I'm also trying to create something like your setup. We could definitely 
> > use something for linux like camtwist on OSX. It should be easily doable 
> > with gstreamer and v4l2loopback. It's quite tricky to get stuff like 
> > this working with gst-launch. I just played a bit with pipeviz and 
> > imediatelly got two streams working with the videomixer.
> > 
> > https://github.com/virinext/pipeviz
> > 
> > Rg,
> > Arnaud
> 
> How does my pipeline fail for you?
> If it fails on v4l2src, try autoviedosrc instead.
> If it fails on ximagesrc, it could be because you have the wrong window 
> id?
> You can drop the videocrop this is to extract the portion of the webcam 
> video of interest to me (zooming in) - and with it you can drop the 
> videoscale and caps to rescale the ximagesrc.
> You can drop the alpha, it should work similarly, albeit without green 
> screen replacement, but that would test the pipeline with more 
> simplicity.
> Check your window ids with "wmctrl -l".
> 
> 
> On Wed, 8 Apr 2020, at 17:14, Desouza, Ederson wrote:
> > Your pipeline does work for me (I just need to scale v4l2src output, as
> > it doesn't output a big enough video for you parameters). I'm afraid
> > I'm out of ideas now... =/
> 
> Different webcams, I suppose. Mine is a 1080p.
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