import sys, time, copy
import gi
gi.require_version('Gst', '1.0')
from gi.repository import GObject, Gst, GstVideo, Gtk
GObject.threads_init()
Gst.init(None)

class Player():
    def __init__(self):

        # build pipeline
        self.pipeline = Gst.ElementFactory.make('pipeline',"pipeline")
        self.source = Gst.ElementFactory.make('videotestsrc')
        self.capsfilter = Gst.ElementFactory.make('capsfilter')
        self.sink = Gst.ElementFactory.make('xvimagesink')
        self.pipeline.add(self.source)
        self.pipeline.add(self.capsfilter)
        self.pipeline.add(self.sink)
        self.source.link(self.capsfilter)
        self.capsfilter.link(self.sink)
        self.capsfilter.get_static_pad("src").add_probe(Gst.PadProbeType.BUFFER, self.cbBufferAtSource)
        self.capsfilter.set_property("caps", Gst.caps_from_string("video/x-raw,width=320,height=240,framerate=(fraction)1/1,format=I420"))
        self.pipeline.set_state(Gst.State.PLAYING)

    def cbBufferAtSource(self, argElement, argPadProbeInfo):
        buffer = argPadProbeInfo.get_buffer()
        print "Received a buffer (pts: %d). Adding metadata!" % (buffer.pts)
        # Get a fresh VideoCropMeta struct
        videoCropMetaInstance = GstVideo.VideoCropMeta()
        # Using the next statement we can see that GstVideo.VideoCropMeta() is indeed the proper struct exposing x, y, width, height as expected.
        #print dir(videoCropMetaInstance)
        videoCropMetaInstance.x = 20
        videoCropMetaInstance.y = 20
        videoCropMetaInstance.width = 20
        videoCropMetaInstance.height = 20
        # Get Gst.MetaInfo from GstVideoCropMeta instance
        videoCropMetaInstanceInfo = videoCropMetaInstance.get_info()
        # Add metadata to buffer
        meta = buffer.add_meta(videoCropMetaInstanceInfo, 0)
        # Print our tags which read correctly: ['video', 'size', 'orientation']
        print "API tags: ", meta.api_type_get_tags(videoCropMetaInstanceInfo.api)
        # Print the memory address of our metadata and the type (Gst.Meta)
        print "Gst.Meta memory address: ", meta
        print "Type of meta:", type(meta)
        # Try to get back our Gst.Meta from our buffer
        test = (buffer.get_meta(videoCropMetaInstanceInfo.api))
        print "Gst.Meta memory address recovered from GstBuffer: ", test
        # How to proceed from here?
        # Set .x and .y on meta? That doesn't work
        print "*"*30
        return Gst.PadProbeReturn.OK

if __name__ == '__main__':
    GObject.threads_init()
    Player()
    while(True):
        Gtk.main_iteration_do(True)