mixer, libao: add proper mute control

The mixer frontend code can now make use of a proper system mixer mute
toggle, if the audio output driver supports it.

The consequence is that, if support is available, mplayer will no longer
temporarily set the system volume to 0 if mute is enabled.

Generally, the code now deals with the following combinations of available
AO features:
- software volume control forced by user (--softvol / soft_vol flag)
  => if enabled, never touch the "hardware" controls
- "hardware"/driver volume control available (whether
  AOCONTROL_GET/SET_VOLUME works)
  => if not available, enable volume controls by enabling softvol
- "hardware"/driver mute control (AOCONTROL_GET/SET_MUTE)
  => if not available, emulate by setting volume to 0
- whether the volume+mute controls are kept or not when the AO is closed
  (indicated by ao->no_persistent_volume)
  => if not persistent, restore the volume/mute next time the AO is opened

1 files changed, 11 insertions, 2 deletions

diff --git a/libao2/audio_out.h b/libao2/audio_out.h
index a8efc92069..c5ddb5bf60 100644
--- a/libao2/audio_out.h
+++ b/libao2/audio_out.h
@@ -97,10 +97,19 @@ void list_audio_out(void);
 #define AOCONTROL_SET_DEVICE 1
 #define AOCONTROL_GET_DEVICE 2
 #define AOCONTROL_QUERY_FORMAT 3 /* test for availabilty of a format */
+// Uses ao_control_vol_t* as arg.
+// If the volume controls are joint, the average of both volumes should be used.
 #define AOCONTROL_GET_VOLUME 4
 #define AOCONTROL_SET_VOLUME 5
-#define AOCONTROL_SET_PLUGIN_DRIVER 6
-#define AOCONTROL_SET_PLUGIN_LIST 7
+// Uses ao_control_vol_t* as arg.
+// left==0.0f means muted, left==1.0f means not muted (right likewise)
+// Other values between are invalid.
+// If the mtue controls are joint, the output should be muted if either of the
+// two channels are muted.
+#define AOCONTROL_GET_MUTE 6
+#define AOCONTROL_SET_MUTE 7
+#define AOCONTROL_SET_PLUGIN_DRIVER 8
+#define AOCONTROL_SET_PLUGIN_LIST 9
 
 #define AOPLAY_FINAL_CHUNK 1