libvlc: add corked and uncorked events (fixes #14444)

This exposes (audio) policy cork events to LibVLC applications. The
intended usage is for applications to pause/resume playback.

We decided against pausing and resuming automatically as it would most
likely confuse the playback state machine of existing applications. By
default, the OS decides might either mute or duck the audio stream.

Cc: Harald Sitter <sitter@kde.org>

include/vlc/libvlc_events.h

@@ -77,6 +77,8 @@ enum libvlc_event_e {
     libvlc_MediaPlayerESAdded,
     libvlc_MediaPlayerESDeleted,
     libvlc_MediaPlayerESSelected,
+    libvlc_MediaPlayerCorked,
+    libvlc_MediaPlayerUncorked,
 
     libvlc_MediaListItemAdded=0x200,
     libvlc_MediaListWillAddItem,

lib/event.c

@@ -283,6 +283,8 @@ static const event_name_t event_list[] = {
     DEF(MediaPlayerESAdded)
     DEF(MediaPlayerESDeleted)
     DEF(MediaPlayerESSelected)
+    DEF(MediaPlayerCorked)
+    DEF(MediaPlayerUncorked)
 
     DEF(MediaListItemAdded)
     DEF(MediaListWillAddItem)

lib/media_player.c

@@ -67,6 +67,10 @@ input_es_selected( vlc_object_t * p_this, char const * psz_cmd,
                    vlc_value_t oldval, vlc_value_t newval,
                    void * p_userdata );
 
+static int
+corks_changed(vlc_object_t *obj, const char *name, vlc_value_t old,
+              vlc_value_t cur, void *opaque);
+
 static void
 add_es_callbacks( input_thread_t *p_input_thread, libvlc_media_player_t *p_mi );
 
@@ -462,6 +466,23 @@ static int snapshot_was_taken(vlc_object_t *p_this, char const *psz_cmd,
     return VLC_SUCCESS;
 }
 
+static int corks_changed(vlc_object_t *obj, const char *name, vlc_value_t old,
+                         vlc_value_t cur, void *opaque)
+{
+    libvlc_media_player_t *mp = (libvlc_media_player_t *)obj;
+
+    if (!old.i_int != !cur.i_int)
+    {
+        libvlc_event_t event;
+
+        event.type = cur.i_int ? libvlc_MediaPlayerCorked
+                               : libvlc_MediaPlayerUncorked;
+        libvlc_event_send(mp->p_event_manager, &event);
+    }
+    VLC_UNUSED(name); VLC_UNUSED(opaque);
+    return VLC_SUCCESS;
+}
+
 /**************************************************************************
  * Create a Media Instance object.
  *
@@ -637,6 +658,10 @@ libvlc_media_player_new( libvlc_instance_t *instance )
     register_event(mp, ESAdded);
     register_event(mp, ESDeleted);
     register_event(mp, ESSelected);
+    register_event(mp, Corked);
+    register_event(mp, Uncorked);
+
+    var_AddCallback(mp, "corks", corks_changed, NULL);
 
     /* Snapshot initialization */
     register_event(mp, SnapshotTaken);
@@ -687,6 +712,9 @@ static void libvlc_media_player_destroy( libvlc_media_player_t *p_mi )
     var_DelCallback( p_mi->p_libvlc,
                      "snapshot-file", snapshot_was_taken, p_mi );
 
+    /* Detach callback from the media player / input manager object */
+    var_DelCallback( p_mi, "corks", corks_changed, NULL );
+
     /* No need for lock_input() because no other threads knows us anymore */
     if( p_mi->input.p_thread )
         release_input_thread(p_mi);