lib: add libvlc_audio_output_device_get()

This function gets the active device identifier for the current
audio output, if there is one, and is the complementary function
to libvlc_audio_output_device_set().
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

NEWS

@@ -87,6 +87,8 @@ libVLC:
  * Add libvlc_media_get_codec_description to get a human readable description of a codec
  * Add libvlc_MediaListEndReached Event to get notified when a media list reached the end
  * Add libvlc_media_parse_with_options that uses a flag to specify parse options
+ * Add libvlc_audio_output_device_get to get the currently selected audio output device
+   identifier (if there is one available)
 
 
 Changes between 2.1.x and 2.2.0:

include/vlc/libvlc_media_player.h

@@ -1570,6 +1570,30 @@ LIBVLC_API void libvlc_audio_output_device_set( libvlc_media_player_t *mp,
                                                 const char *module,
                                                 const char *device_id );
 
+/**
+ * Get the current audio output device identifier.
+ *
+ * This complements libvlc_audio_output_device_set().
+ *
+ * \warning The initial value for the current audio output device identifier
+ * may not be set or may be some unknown value. A LibVLC application should
+ * compare this value against the known device identifiers (e.g. those that
+ * were previously retrieved by a call to libvlc_audio_output_device_enum or
+ * libvlc_audio_output_device_list_get) to find the current audio output device.
+ *
+ * It is possible that the selected audio output device changes (an external
+ * change) without a call to libvlc_audio_output_device_set. That may make this
+ * method unsuitable to use if a LibVLC application is attempting to track
+ * dynamic audio device changes as they happen.
+ *
+ * \param mp media player
+ * \return the current audio output device identifier
+ *         NULL if no device is selected or in case of error
+ *         (the result must be released with free() or libvlc_free()).
+ * \version LibVLC 3.0.0 or later.
+ */
+LIBVLC_API char *libvlc_audio_output_device_get( libvlc_media_player_t *mp );
+
 /**
  * Stub for backward compatibility.
  * \return always -1.

lib/audio.c

@@ -277,6 +277,19 @@ void libvlc_audio_output_device_set( libvlc_media_player_t *mp,
     vlc_object_release( aout );
 }
 
+char *libvlc_audio_output_device_get( libvlc_media_player_t *mp )
+{
+    audio_output_t *aout = GetAOut( mp );
+    if( aout == NULL )
+        return NULL;
+
+    char *devid = aout_DeviceGet( aout );
+
+    vlc_object_release( aout );
+
+    return devid;
+}
+
 int libvlc_audio_output_get_device_type( libvlc_media_player_t *mp )
 {
     (void) mp;

lib/libvlc.sym

@@ -15,6 +15,7 @@ libvlc_audio_equalizer_release
 libvlc_audio_equalizer_set_amp_at_index
 libvlc_audio_equalizer_set_preamp
 libvlc_audio_output_device_count
+libvlc_audio_output_device_get
 libvlc_audio_output_device_enum
 libvlc_audio_output_device_id
 libvlc_audio_output_device_list_get