Gstreamer compositing using the GstvideoMixerPad properties

Few weeks agio I posted my notes about picture-in-picture compositing in Gstreamer using nothing else than the gst-launch command line tool. I also wrote that I could not figure out how to use the xpos, ypos, zorder properties of the GstVideoMixerPad element. I got a comment on this note from Jan Schmidt telling that these properties can not be used with gst-launch but are easily accessible from Python. He also gave a very cool example that shows how to use it.

Here is a video showing the example in action:

You can also watch the video on YouTube.

And here is the Python example from Jan:

  import gobject; gobject.threads_init()
  import pygst; pygst.require("0.10")
  import gst
  p = gst.parse_launch ("""videomixer name=mix ! ffmpegcolorspace ! xvimagesink
        videotestsrc pattern="snow" ! video/x-raw-yuv, framerate=10/1, width=200, height=150 ! mix.sink_0
        videotestsrc ! video/x-raw-yuv, framerate=10/1, width=640, height=360 ! mix.sink_1
  m = p.get_by_name ("mix")
  s0 = m.get_pad ("sink_0")
  s0.set_property ("xpos", 100)
  control = gst.Controller(s0, "ypos", "alpha")
  control.set_interpolation_mode("ypos", gst.INTERPOLATE_LINEAR)
  control.set_interpolation_mode("alpha", gst.INTERPOLATE_LINEAR)
  control.set("ypos", 0, 0); control.set("ypos", 5 * gst.SECOND, 200)
  control.set("alpha", 0, 0); control.set("alpha", 5 * gst.SECOND, 1.0)
  p.set_state (gst.STATE_PLAYING)