softvol, ao_pulse: prefer ao_pulse volume control by default

--softvol is enabled by default. For most audio outputs, this is a good
thing, as they have either their own (bad) soft volume implementation,
or control the system mixer. With ao_pulse, the situation is a bit
different: it supports per-application volume (i.e. volume control is
not really global). More importantly, ao_pulse uses a rather large audio
buffer, and changing the volume with mplayer's volume filter has a large
delay. With the native ao_pulse volume control, it's instant, because
PulseAudio's audio filtering happens at a later stage in its processing
pipeline (inaccessible for mplayer).

This means native volume control should really be allowed for ao_pulse,
while it's the reverse for other audio outputs. Make --softvol a choice
option, and add a new "auto" choice. This is default and will use PA's
volume control with ao_pulse, and mplayer's volume filter otherwise
(i.e. the old softvol behavior).

DOCS/man/en/options.rst

@@ -1741,9 +1741,19 @@
     timing is imprecise and you cannot use the RTC either. Comes at the
     price of higher CPU consumption.
 
---no-softvol
-    Try to use the sound card mixer (if available), instead of using the volume
-    audio filter.
+--softvol=<mode>
+    Control whether to use the volume controls of the audio output driver, or
+    the internal mplayer volume filter.
+
+    :no:    prefer audio driver controls, use the volume filter only if
+            absolutely needed
+    :yes:   always use the volume filter
+    :auto:  prefer the volume filter if the audio driver uses the system mixer (default)
+
+    The intention with ``auto`` is to avoid changing system mixer settings with
+    default settings. mplayer is a video player, not a mixer panel. On the other
+    hand, mixer controls should be used for sound servers like PulseAudio, which
+    provide per-application volume.
 
 --softvol-max=<10.0-10000.0>
     Set the maximum amplification level in percent (default: 200). A value of

cfg-mplayer.h

@@ -587,7 +587,10 @@ const m_option_t mplayer_opts[]={
 
     OPT_STRING("mixer", mixer_device, 0),
     OPT_STRING("mixer-channel", mixer_channel, 0),
-    OPT_MAKE_FLAGS("softvol", softvol, 0),
+    OPT_CHOICE("softvol", softvol, 0,
+               ({"no", SOFTVOL_NO},
+                {"yes", SOFTVOL_YES},
+                {"auto", SOFTVOL_AUTO})),
     OPT_FLOATRANGE("softvol-max", softvol_max, 0, 10, 10000),
     {"volstep", &volstep, CONF_TYPE_INT, CONF_RANGE, 0, 100, NULL},
     {"volume", &start_volume, CONF_TYPE_FLOAT, CONF_RANGE, -1, 10000, NULL},

defaultopts.c

@@ -3,6 +3,7 @@
 #include "config.h"
 #include "defaultopts.h"
 #include "options.h"
+#include "mixer.h"
 
 void set_default_mplayer_options(struct MPOpts *opts)
 {
@@ -10,7 +11,7 @@ void set_default_mplayer_options(struct MPOpts *opts)
         .audio_driver_list = NULL,
         .video_driver_list = NULL,
         .fixed_vo = 1,
-        .softvol = 1,
+        .softvol = SOFTVOL_AUTO,
         .softvol_max = 200,
         .ao_buffersize = -1,
         .vo_wintitle = "mplayer - ${filename}",

libao2/ao_pulse.c

@@ -184,6 +184,8 @@ static int init(struct ao *ao, char *params)
     struct priv *priv = talloc_zero(ao, struct priv);
     ao->priv = priv;
 
+    ao->per_application_mixer = true;
+
     if (params) {
         devarg = strdup(params);
         sink = strchr(devarg, ':');

libao2/audio_out.h

@@ -104,6 +104,7 @@ struct ao {
     bool initialized;
     bool untimed;
     bool no_persistent_volume;
+    bool per_application_mixer;
     const struct ao_driver *driver;
     void *priv;
     struct encode_lavc_context *encode_lavc_ctx;

mixer.c

@@ -32,10 +32,15 @@ static void checkvolume(struct mixer *mixer)
     if (!mixer->ao)
         return;
 
+    if (mixer->softvol == SOFTVOL_AUTO) {
+        mixer->softvol = mixer->ao->per_application_mixer
+                         ? SOFTVOL_NO : SOFTVOL_YES;
+    }
+
     ao_control_vol_t vol;
     if (mixer->softvol || CONTROL_OK != ao_control(mixer->ao,
                                                 AOCONTROL_GET_VOLUME, &vol)) {
-        mixer->softvol = true;
+        mixer->softvol = SOFTVOL_YES;
         if (!mixer->afilter)
             return;
         float db_vals[AF_NCH];

mixer.h

@@ -24,11 +24,17 @@
 #include "libaf/af.h"
 #include "libao2/audio_out.h"
 
+enum {
+    SOFTVOL_NO = 0,
+    SOFTVOL_YES = 1,
+    SOFTVOL_AUTO = 2,
+};
+
 typedef struct mixer {
     struct ao *ao;
     af_stream_t *afilter;
     int volstep;
-    bool softvol;
+    int softvol;
     float softvol_max;
     bool muted;
     bool muted_by_us;