Update

subprojects/gst-python/examples/plugins/python/exampleTransform.py

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+#!/usr/bin/python3
+# exampleTransform.py
+# 2019 Daniel Klamt <graphics@pengutronix.de>
+
+# Inverts a grayscale image in place, requires numpy.
+#
+# gst-launch-1.0 videotestsrc ! ExampleTransform ! videoconvert ! xvimagesink
+
+import gi
+gi.require_version('Gst', '1.0')
+gi.require_version('GstBase', '1.0')
+gi.require_version('GstVideo', '1.0')
+
+from gi.repository import Gst, GObject, GstBase, GstVideo
+
+import numpy as np
+
+Gst.init(None)
+FIXED_CAPS = Gst.Caps.from_string('video/x-raw,format=GRAY8,width=[1,2147483647],height=[1,2147483647]')
+
+class ExampleTransform(GstBase.BaseTransform):
+    __gstmetadata__ = ('ExampleTransform Python','Transform',
+                      'example gst-python element that can modify the buffer gst-launch-1.0 videotestsrc ! ExampleTransform ! videoconvert ! xvimagesink', 'dkl')
+
+    __gsttemplates__ = (Gst.PadTemplate.new("src",
+                                           Gst.PadDirection.SRC,
+                                           Gst.PadPresence.ALWAYS,
+                                           FIXED_CAPS),
+                       Gst.PadTemplate.new("sink",
+                                           Gst.PadDirection.SINK,
+                                           Gst.PadPresence.ALWAYS,
+                                           FIXED_CAPS))
+
+    def do_set_caps(self, incaps, outcaps):
+        struct = incaps.get_structure(0)
+        self.width = struct.get_int("width").value
+        self.height = struct.get_int("height").value
+        return True
+
+    def do_transform_ip(self, buf):
+        try:
+            with buf.map(Gst.MapFlags.READ | Gst.MapFlags.WRITE) as info:
+                # Create a NumPy ndarray from the memoryview and modify it in place:
+                A = np.ndarray(shape = (self.height, self.width), dtype = np.uint8, buffer = info.data)
+                A[:] = np.invert(A)
+
+                return Gst.FlowReturn.OK
+        except Gst.MapError as e:
+            Gst.error("Mapping error: %s" % e)
+            return Gst.FlowReturn.ERROR
+
+GObject.type_register(ExampleTransform)
+__gstelementfactory__ = ("ExampleTransform", Gst.Rank.NONE, ExampleTransform)