mixer: Add mixer API

docs/api/index.rst

@@ -21,6 +21,7 @@ API reference
     backends
     core
     audio
+    mixer
     frontends
     commands
     ext

docs/api/mixer.rst

@@ -0,0 +1,17 @@
+.. _mixer-api:
+
+***************
+Audio mixer API
+***************
+
+.. module:: mopidy.mixer
+    :synopsis: The audio mixer API
+
+.. autoclass:: mopidy.mixer.Mixer
+    :members:
+
+
+Mixer implementations
+=====================
+
+- TODO

mopidy/mixer.py

@@ -0,0 +1,51 @@
+from __future__ import unicode_literals
+
+
+class Mixer(object):
+    """Audio mixer API"""
+
+    def get_volume(self):
+        """
+        Get volume level of the mixer.
+
+        Example values:
+
+        0:
+            Minimum volume, usually silent.
+        100:
+            Max volume.
+        :class:`None`:
+            Volume is unknown.
+
+        :rtype: int in range [0..100] or :class:`None`
+        """
+        return None
+
+    def set_volume(self, volume):
+        """
+        Set volume level of the mixer.
+
+        :param volume: Volume in the range [0..100]
+        :type volume: int
+        :rtype: :class:`True` if success, :class:`False` if failure
+        """
+        return False
+
+    def get_mute(self):
+        """
+        Get mute status of the mixer.
+
+        :rtype: :class:`True` if muted, :class:`False` if unmuted,
+          :class:`None` if unknown.
+        """
+        return None
+
+    def set_mute(self, muted):
+        """
+        Mute or unmute the mixer.
+
+        :param muted: :class:`True` to mute, :class:`False` to unmute
+        :type muted: bool
+        :rtype: :class:`True` if success, :class:`False` if failure
+        """
+        return False