audio: Add about to finish callback support

mopidy/audio/actor.py

@@ -58,6 +58,7 @@ class Audio(pykka.ThreadingActor):
 
         self._playbin = None
         self._signal_ids = {}  # {(element, event): signal_id}
+        self._about_to_finish_callback = None
 
         self._mixer = None
         self._mixer_track = None
@@ -108,15 +109,15 @@ class Audio(pykka.ThreadingActor):
 
     def _on_about_to_finish(self, element):
         source, self._appsrc = self._appsrc, None
-        if source is None:
-            return
-        self._appsrc_caps = None
+        if source is not None:
+            self._appsrc_caps = None
+            self._disconnect(source, 'need-data')
+            self._disconnect(source, 'enough-data')
+            self._disconnect(source, 'seek-data')
 
-        self._disconnect(source, 'need-data')
-        self._disconnect(source, 'enough-data')
-        self._disconnect(source, 'seek-data')
-
-        logger.debug('Ready to switch to new stream')
+        if self._about_to_finish_callback:
+            logger.debug('Calling about to finish callback.')
+            self._about_to_finish_callback()
 
     def _on_new_source(self, element, pad):
         uri = element.get_property('uri')
@@ -432,6 +433,19 @@ class Audio(pykka.ThreadingActor):
         # TODO: replace this with emit_data(None)?
         self._playbin.get_property('source').emit('end-of-stream')
 
+    def set_about_to_finish_callback(self, callback):
+        """
+        Configure audio to use an about to finish callback.
+
+        This should be used to achieve gapless playback. For this to work the
+        callback *MUST* call :meth:`set_uri` with the new URI to play and
+        block until this call has been made. :meth:`prepare_change` is not
+        needed before :meth:`set_uri` in this one special case.
+
+        :param callable callback: Callback to run when we need the next URI.
+        """
+        self._about_to_finish_callback = callback
+
     def get_position(self):
         """
         Get position in milliseconds.

tests/audio/test_actor.py

@@ -324,6 +324,45 @@ class AudioEventTest(unittest.TestCase):
         if not event.wait(timeout=5.0):
             self.fail('End of stream not reached within deadline')
 
+    # Make sure that gapless really works:
+
+    def test_gapless(self, send_mock):
+        song2_uri = path_to_uri(path_to_data_dir('song2.wav'))
+
+        uris = [song2_uri]
+        events = []
+        done = threading.Event()
+
+        def callback():
+            if uris:
+                self.audio.set_uri(uris.pop()).get()
+
+        def send(name, **kwargs):
+            events.append((name, kwargs))
+            if name == 'reached_end_of_stream':
+                done.set()
+
+        send_mock.side_effect = send
+        self.audio.set_about_to_finish_callback(callback).get()
+
+        self.audio.prepare_change()
+        self.audio.set_uri(self.song_uri)
+        self.audio.start_playback()
+        self.audio.wait_for_state_change().get()
+
+        if not done.wait(timeout=5.0):
+            self.fail('EOS not received')
+
+        excepted = [
+            ('position_changed', {'position': 0}),
+            ('stream_changed', {'uri': self.song_uri}),
+            ('state_changed', {'old_state': PlaybackState.STOPPED,
+                               'new_state': PlaybackState.PLAYING}),
+            ('position_changed', {'position': 0}),
+            ('stream_changed', {'uri': song2_uri}),
+            ('reached_end_of_stream', {})]
+        self.assertEqual(excepted, events)
+
 
 class AudioStateTest(unittest.TestCase):
     def setUp(self):