Examples: add mixer plugin example

examples/README.md

@@ -0,0 +1,11 @@
+# Dependencies
+
+Some of the examples require external python dependencies, for this purpose
+an illustrative requirements.txt is provided, with annotations documenting
+which example requires a dependency.
+
+You can install all the dependencies with:
+
+```
+python3 -m pip install -r requirements.txt --user
+```

examples/plugins/python/mixer.py

@@ -0,0 +1,104 @@
+'''
+Simple mixer element, accepts 320 x 240 RGBA at 30 fps
+on any number of sinkpads.
+
+Requires PIL (Python Imaging Library)
+
+Example pipeline:
+
+gst-launch-1.0 py_videomixer name=mixer ! videoconvert ! autovideosink \
+        videotestsrc ! mixer. \
+        videotestsrc pattern=ball ! mixer. \
+        videotestsrc pattern=snow ! mixer.
+'''
+
+import gi
+
+gi.require_version('Gst', '1.0')
+gi.require_version('GstBase', '1.0')
+gi.require_version('GObject', '2.0')
+
+from gi.repository import Gst, GObject, GstBase
+
+Gst.init(None)
+
+try:
+    from PIL import Image
+except ImportError:
+    Gst.error('py_videomixer requires PIL')
+    raise
+
+# Completely fixed input / output
+ICAPS = Gst.Caps(Gst.Structure('video/x-raw',
+                               format='RGBA',
+                               width=320,
+                               height=240,
+                               framerate=Gst.Fraction(30, 1)))
+
+OCAPS = Gst.Caps(Gst.Structure('video/x-raw',
+                               format='RGBA',
+                               width=320,
+                               height=240,
+                               framerate=Gst.Fraction(30, 1)))
+
+class BlendData:
+    def __init__(self, outimg):
+        self.outimg = outimg
+        self.pts = 0
+        self.eos = True
+
+class Videomixer(GstBase.Aggregator):
+    __gstmetadata__ = ('Videomixer','Video/Mixer', \
+                      'Python video mixer', 'Mathieu Duponchelle')
+
+    __gsttemplates__ = (
+            Gst.PadTemplate.new_with_gtype("sink_%u",
+                                Gst.PadDirection.SINK,
+                                Gst.PadPresence.REQUEST,
+                                ICAPS,
+                                GstBase.AggregatorPad.__gtype__),
+            Gst.PadTemplate.new_with_gtype("src",
+                                Gst.PadDirection.SRC,
+                                Gst.PadPresence.ALWAYS,
+                                OCAPS,
+                                GstBase.AggregatorPad.__gtype__)
+    )
+
+    def mix_buffers(self, agg, pad, bdata):
+        buf = pad.pop_buffer()
+        _, info = buf.map(Gst.MapFlags.READ)
+
+        img = Image.frombuffer('RGBA', (320, 240), info.data, "raw", 'RGBA', 0, 1)
+
+        bdata.outimg = Image.blend(bdata.outimg, img, alpha=0.5)
+        bdata.pts = buf.pts
+
+        buf.unmap(info)
+
+        bdata.eos = False
+
+        return True
+
+    def do_aggregate(self, timeout):
+        outimg = Image.new('RGBA', (320, 240), 0x00000000)
+
+        bdata = BlendData(outimg)
+
+        self.foreach_sink_pad(self.mix_buffers, bdata)
+
+        data = bdata.outimg.tobytes()
+
+        outbuf = Gst.Buffer.new_allocate(None, len(data), None)
+        outbuf.fill(0, data)
+        outbuf.pts = bdata.pts
+        self.finish_buffer (outbuf)
+
+        # We are EOS when no pad was ready to be aggregated,
+        # this would obviously not work for live
+        if bdata.eos:
+            return Gst.FlowReturn.EOS
+
+        return Gst.FlowReturn.OK
+
+GObject.type_register(Videomixer)
+__gstelementfactory__ = ("py_videomixer", Gst.Rank.NONE, Videomixer)

examples/requirements.txt

@@ -0,0 +1,2 @@
+# py_videomixer plugin
+Pillow >= 5.1.0