Using Gstreamer to capture screen and show it in a window?

Question

I need to capture the screen of the second display and "monitor" it in the main display, inside a window (scaled at x0.5 and with neighbor interpolation because I prefer performance against quality). From this link, I've got this screencast command:

gst-launch ximagesrc ! ffmpegcolorspace ! queue \
! vp8enc quality=10 speed=2 ! mux. alsasrc ! audio/x-raw-int ! queue \
! audioconvert ! vorbisenc ! mux. webmmux name=mux \
! filesink location=screencast.webm

... but it capture to a file (not a window), it's missing the scale and interpolation type, the sounds is not necessary, etc.

As I'm familiar with libav, what I'm looking for is something similar to this:

avconv -f x11grab -r 30 -s 1280x1024 -i :0.1 -c:v mpeg4 -b:v 1000k \
-vf "hflip" -vf "scale=640:480" -sws_flags "neighbor" -f avi - | avplay -i -

... I would use it, but it has some problems with the framerate (asked here). So, I'm looking for an alternative in Gstreamer.

Helicoid

please provide mcve, if you have something and its not working we can move on with answers. But I will give you a hint, good luck – Highup

@otopolsky: I edited the question, trying to provide mcve. I had already searched for you hint and that's how I had found the gst-launch command that I just added. – Helicoid

Answer 1

Here is the gst-launch command:

gst-launch-1.0 ximagesrc startx=1280 use-damage=0 ! video/x-raw,framerate=30/1 ! videoscale method=0 ! video/x-raw,width=640,height=480  ! ximagesink

Explanation:

parameter startx = start recording from "pixel column" 1280 - that is if you have two 1280 width monitors it will start with the one on the right side.

parameter use-damage set to 0 = do not use XDamage. damage counts only differences between subsequent frames which is apparantly quite CPU demanding.

element ximagesink = X server created window as output - its less CPU demanding than glimagesink (opengl accelerated window).

element videoscale parameter method to 0 meaning nearest neighbor as suggested by Mario Mey in comment. This resulted for me in CPU save from 17% to 12%.

There is also configurable fps and height/width of display window(I think its clear enough).

Highup

This is what I need, thank you! I had to use ximagesink instead of glimagesink (it says WARNING: erroneous pipeline: no element "glimagesink"). And I added "method=0" to use a nearest-neighbour interpolation to videoscale, to make it even cheaper (from here) – Helicoid

thanks @MarioMey I updated the answer. so you are missing glimagesink. But funny enough - I made some tests and its much faster with ximagesink than glimagesink - I will further edit my answer. – Highup

I was trying to swap ximagesink with v4l2sink device=/dev/video1. This doesn't produce any errors, except the "webcam" doesn't actually work in Firefox or Chrome. Any chance you could help? – Rambert

@ratskin well you should create another question for that.. its quite different from this one – Highup

@Highup You're right, and I already did unix.stackexchange.com/questions/528400/… – Rambert