From c23cad5d134df467aa80b997250f18a58fea2ec3 Mon Sep 17 00:00:00 2001
From: Thomas Adamcik <thomas@adamcik.no>
Date: Sat, 13 Feb 2016 22:34:09 +0100
Subject: [PATCH 1/3] audio: Only emit tags changed when tags changed.

Previously we alerted AudioListeners about all new tags, now we filter it down
to just the changed ones. Only real reason for this is that the changed
messages spam the log output making debugging harder.
---
 mopidy/audio/actor.py | 16 +++++++++++++---
 mopidy/audio/tags.py  |  1 +
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/mopidy/audio/actor.py b/mopidy/audio/actor.py
index f825a768..ea4a6ed9 100644
--- a/mopidy/audio/actor.py
+++ b/mopidy/audio/actor.py
@@ -326,9 +326,19 @@ class _Handler(object):
     def on_tag(self, taglist):
         tags = tags_lib.convert_taglist(taglist)
         gst_logger.debug('Got TAG bus message: tags=%r', dict(tags))
-        self._audio._tags.update(tags)
-        logger.debug('Audio event: tags_changed(tags=%r)', tags.keys())
-        AudioListener.send('tags_changed', tags=tags.keys())
+
+        # TODO: Add proper tests for only emitting changed tags.
+        unique = object()
+        changed = []
+        for key, value in tags.items():
+            # Update any tags that changed, and store changed keys.
+            if self._audio._tags.get(key, unique) != value:
+                self._audio._tags[key] = value
+                changed.append(key)
+
+        if changed:
+            logger.debug('Audio event: tags_changed(tags=%r)', changed)
+            AudioListener.send('tags_changed', tags=changed)
 
     def on_missing_plugin(self, msg):
         desc = GstPbutils.missing_plugin_message_get_description(msg)
diff --git a/mopidy/audio/tags.py b/mopidy/audio/tags.py
index 62784bc0..38a0bac9 100644
--- a/mopidy/audio/tags.py
+++ b/mopidy/audio/tags.py
@@ -58,6 +58,7 @@ gstreamer-GstTagList.html
                     log.TRACE_LOG_LEVEL,
                     'Ignoring unknown tag data: %r = %r', tag, value)
 
+    # TODO: dict(result) to not leak the defaultdict, or just use setdefault?
     return result
 
 

From b63b3c288add2826b7cb44abefe378ffb4cfc668 Mon Sep 17 00:00:00 2001
From: Thomas Adamcik <thomas@adamcik.no>
Date: Sat, 13 Feb 2016 22:44:31 +0100
Subject: [PATCH 2/3] audio: Postpone tags until after stream-start

When a new URI gets set we create a pending tags dictionary. This gets all the
tags until stream-start, at which point they are all emitted at once. During
track playback tags works as before.

This ensure we don't prematurely tell clients about metadata changes.
---
 mopidy/audio/actor.py | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/mopidy/audio/actor.py b/mopidy/audio/actor.py
index ea4a6ed9..64300ff9 100644
--- a/mopidy/audio/actor.py
+++ b/mopidy/audio/actor.py
@@ -327,6 +327,11 @@ class _Handler(object):
         tags = tags_lib.convert_taglist(taglist)
         gst_logger.debug('Got TAG bus message: tags=%r', dict(tags))
 
+        # Postpone emitting tags until stream start.
+        if self._audio._pending_tags is not None:
+            self._audio._pending_tags.update(tags)
+            return
+
         # TODO: Add proper tests for only emitting changed tags.
         unique = object()
         changed = []
@@ -359,6 +364,14 @@ class _Handler(object):
         logger.debug('Audio event: stream_changed(uri=%r)', uri)
         AudioListener.send('stream_changed', uri=uri)
 
+        # Emit any postponed tags that we got after about-to-finish.
+        tags, self._audio._pending_tags = self._audio._pending_tags, None
+        self._audio._tags = tags
+
+        if tags:
+            logger.debug('Audio event: tags_changed(tags=%r)', tags.keys())
+            AudioListener.send('tags_changed', tags=tags.keys())
+
     def on_segment(self, segment):
         gst_logger.debug(
             'Got SEGMENT pad event: '
@@ -396,6 +409,7 @@ class Audio(pykka.ThreadingActor):
         self._buffering = False
         self._tags = {}
         self._pending_uri = None
+        self._pending_tags = None
 
         self._playbin = None
         self._outputs = None
@@ -546,8 +560,8 @@ class Audio(pykka.ThreadingActor):
         else:
             current_volume = None
 
-        self._tags = {}  # TODO: add test for this somehow
         self._pending_uri = uri
+        self._pending_tags = {}
         self._playbin.set_property('uri', uri)
 
         if self.mixer is not None and current_volume is not None:

From d20621c801f56eaac4eb675879ba0cecab82f7e2 Mon Sep 17 00:00:00 2001
From: Thomas Adamcik <thomas@adamcik.no>
Date: Sun, 14 Feb 2016 12:35:16 +0100
Subject: [PATCH 3/3] docs: Add changelog entry for tags_changed

---
 docs/changelog.rst | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/docs/changelog.rst b/docs/changelog.rst
index 32453c13..938e19d6 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -176,6 +176,10 @@ Audio
   time of the GStreamer queue. If you experience buffering before track
   changes, it may help to increase this. Workaround for :issue:`1409`.
 
+- ``tags_changed`` events are only emitted for fields that have changed.
+  Previous behavior was to emit this for all fields received from GStreamer.
+  (PR: :issue:`1439`)
+
 Gapless
 -------