audio: A uri list element.

This element "simply" takes the list of uris that our other elements have
already converted to simpler format, picks the first uri and play it. This
is done by ensuring that we block the right EOS messages, and all new segment
messages from the original sources. With these events blocked we can inject
our own nested uridecodebin to play the uri and push our own data. The nested
uridecodebin is setup with caps('any') to ensure that we don't suddenly demux
and end up with multiple streams by accident.

mopidy/audio/playlists.py

@@ -198,6 +198,49 @@ class XSPFDecoder(BasePlaylistElement):
         return parse_xspf(data)
 
 
+class UriListElement(BasePlaylistElement):
+    __gstdetails__ = ('URIListDemuxer',
+                      'Demuxer',
+                      'Convert a text/uri-list to a stream',
+                      'Mopidy')
+
+    sinktemplate = gst.PadTemplate ('sink',
+        gst.PAD_SINK,
+        gst.PAD_ALWAYS,
+        gst.caps_from_string('text/uri-list'))
+
+    srctemplate = gst.PadTemplate ('src',
+        gst.PAD_SRC,
+        gst.PAD_ALWAYS,
+        gst.caps_new_any())
+
+    ghostsrc = True  # We need to hook this up to our internal decodebin
+
+    __gsttemplates__ = (sinktemplate, srctemplate)
+
+    def __init__(self):
+        super(UriListElement, self).__init__()
+        self.uridecodebin = gst.element_factory_make('uridecodebin')
+        self.uridecodebin.connect('pad-added', self.pad_added)
+        # Limit to anycaps so we get a single stream out, letting other
+        # elmenets downstream figure out actual muxing
+        self.uridecodebin.set_property('caps', gst.caps_new_any())
+
+    def pad_added(self, src, pad):
+        self.src.set_target(pad)
+
+    def handle(self, uris):
+        # TODO: hookup about to finish and errors to rest of uris so we
+        # round robin, only giving up once all have been tried.
+        self.add(self.uridecodebin)
+        self.uridecodebin.set_state(gst.STATE_READY)
+        self.uridecodebin.set_property('uri', uris[0])
+        self.uridecodebin.sync_state_with_parent()
+        return True  # Make sure we consume the EOS that triggered us.
+
+    def convert(self, data):
+        return parse_urilist(data)
+
 
 def register_element(element_class):
     gobject.type_register(element_class)
@@ -209,3 +252,4 @@ def register_elements():
     register_element(M3UDecoder)
     register_element(PLSDecoder)
     register_element(XSPFDecoder)
+    register_element(UriListElement)