This is playing self player gst Pipeline pipeline self source Source b

This is playing:
self.player = gst.Pipeline("pipeline")
self.source = Source("bufsrc", config, track)
decoder = gst.element_factory_make("mad", "mp3-decoder")
conv = gst.element_factory_make("audioconvert", "converter")
sink = gst.element_factory_make("alsasink", "alsa-output")
self.player.add(self.source, decoder, conv, sink)
gst.element_link_many(self.source, decoder, conv, sink)

This is not playing:
self.source = Source("bufsrc", config, track)
self.player = gst.element_factory_make("playbin2")
self.player.add(self.source)
self.player.set_property("uri", "bufsrc:/")