mixer: restore volume with playback resume

Note that this is intentionally never done if the AO or softvolume is
different, or if the current volume control method is thought to control
system wide volume (such as ALSA) or otherwise user controllable (such
as PulseAudio). The intention is to keep things robust and to avoid
messing with the user's audio settings as far as possible, while still
providing the ability to resume volume if it makes sense.

DOCS/man/en/options.rst

@@ -2596,6 +2596,18 @@
     Set the startup volume. A value of -1 (the default) will not change the
     volume. See also ``--softvol``.
 
+``--volume-restore-data=<string>``
+    Used internally for use by playback resume (e.g. with ``quit_watch_later``).
+    Restoring value has to be done carefully, because different AOs as well as
+    softvol can have different value ranges, and we don't want to restore
+    volume if setting the volume changes it system wide. The normal options
+    (like ``--volume``) would always set the volume. This option was added for
+    restoring volume in a safer way (by storing the method used to set the
+    volume), and is not generally useful. Its semantics are considered private
+    to mpv.
+
+    Do not use.
+
 ``--wid=<ID>``
     (X11 and Windows only)
     This tells mpv to attach to an existing window. The ID is interpreted as

audio/mixer.c

@@ -17,6 +17,7 @@
  */
 
 #include <string.h>
+#include <stdio.h>
 
 #include <libavutil/common.h>
 
@@ -24,6 +25,7 @@
 #include "audio/out/ao.h"
 #include "audio/filter/af.h"
 #include "mpvcore/mp_msg.h"
+#include "talloc.h"
 #include "mixer.h"
 
 void mixer_init(struct mixer *mixer, struct MPOpts *opts)
@@ -228,6 +230,14 @@ void mixer_setbalance(mixer_t *mixer, float val)
                             AF_CONTROL_PAN_BALANCE | AF_CONTROL_SET, &val);
 }
 
+char *mixer_get_volume_restore_data(struct mixer *mixer)
+{
+    if (!mixer->driver[0])
+        return NULL;
+    return talloc_asprintf(NULL, "%s:%f:%f:%d", mixer->driver, mixer->vol_l,
+                           mixer->vol_r, mixer->muted_by_us);
+}
+
 static void probe_softvol(struct mixer *mixer)
 {
     if (mixer->opts->softvol == SOFTVOL_AUTO) {
@@ -286,10 +296,28 @@ static void restore_volume(struct mixer *mixer)
     if (opts->mixer_init_mute >= 0)
         force_mute = opts->mixer_init_mute;
 
+    // Set parameters from playback resume.
+    char *restore_data = mixer->opts->mixer_restore_volume_data;
+    if (restore && restore_data && restore_data[0]) {
+        char drv[40];
+        float v_l, v_r;
+        int m;
+        if (sscanf(restore_data, "%39[^:]:%f:%f:%d", drv, &v_l, &v_r, &m) == 4) {
+            if (strcmp(mixer->driver, drv) == 0) {
+                force_vol_l = v_l;
+                force_vol_r = v_r;
+                force_mute = !!m;
+            }
+        }
+        talloc_free(restore_data);
+        mixer->opts->mixer_restore_volume_data = NULL;
+    }
+
     // Using --volume should not reset the volume on every file (i.e. reinit),
     // OTOH mpv --{ --volume 10 f1.mkv --} --{ --volume 20 f2.mkv --} must work.
     // Resetting the option volumes to "auto" (-1) is easiest. If file local
-    // options (as shown above) are used, these are reset to other values.
+    // options (as shown above) are used, the option handler code will reset
+    // them to other values, and force the volume to be reset as well.
     opts->mixer_init_volume = -1;
     opts->mixer_init_mute = -1;
 

audio/mixer.h

@@ -59,5 +59,6 @@ void mixer_setmute(mixer_t *mixer, bool mute);
 bool mixer_getmute(mixer_t *mixer);
 void mixer_getbalance(mixer_t *mixer, float *bal);
 void mixer_setbalance(mixer_t *mixer, float bal);
+char *mixer_get_volume_restore_data(struct mixer *mixer);
 
 #endif /* MPLAYER_MIXER_H */

mpvcore/command.c

@@ -804,6 +804,21 @@ static int mp_property_mute(m_option_t *prop, int action, void *arg,
     return M_PROPERTY_NOT_IMPLEMENTED;
 }
 
+static int mp_property_volrestore(m_option_t *prop, int action,
+                                   void *arg, MPContext *mpctx)
+{
+    switch (action) {
+    case M_PROPERTY_GET: {
+        char *s = mixer_get_volume_restore_data(&mpctx->mixer);
+        *(char **)arg = s;
+        return s ? M_PROPERTY_OK : M_PROPERTY_UNAVAILABLE;
+    }
+    case M_PROPERTY_SET:
+        return M_PROPERTY_NOT_IMPLEMENTED;
+    }
+    return mp_property_generic_option(prop, action, arg, mpctx);
+}
+
 /// Audio delay (RW)
 static int mp_property_audio_delay(m_option_t *prop, int action,
                                    void *arg, MPContext *mpctx)
@@ -1806,6 +1821,7 @@ static const m_option_t mp_properties[] = {
     M_OPTION_PROPERTY_CUSTOM("aid", mp_property_audio),
     { "balance", mp_property_balance, CONF_TYPE_FLOAT,
       M_OPT_RANGE, -1, 1, NULL },
+    M_OPTION_PROPERTY_CUSTOM("volume-restore-data", mp_property_volrestore),
 
     // Video
     M_OPTION_PROPERTY_CUSTOM("fullscreen", mp_property_fullscreen),

mpvcore/mplayer.c

@@ -809,8 +809,7 @@ static const char *backup_properties[] = {
     "speed",
     "edition",
     "pause",
-    //"volume",
-    //"mute",
+    "volume-restore-data",
     "audio-delay",
     //"balance",
     "fullscreen",

mpvcore/options.c

@@ -565,6 +565,7 @@ const m_option_t mp_opts[] = {
                ({"auto", -1},
                 {"no", 0},
                 {"yes", 1}, {"", 1})),
+    OPT_STRING("volume-restore-data", mixer_restore_volume_data, 0),
     OPT_FLAG("gapless-audio", gapless_audio, 0),
 
     // set screen dimensions (when not detectable or virtual!=visible)

mpvcore/options.h

@@ -51,6 +51,7 @@ typedef struct MPOpts {
     int softvol;
     float mixer_init_volume;
     int mixer_init_mute;
+    char *mixer_restore_volume_data;
     int volstep;
     float softvol_max;
     int gapless_audio;