[MPlayer-dev-eng] [PATCH 2/2] alsa: Better volume control handling, especially for S/PDIF.

[Reimar Döffinger]

If no mixer channel was specified and PCM does not exist, just
pick the first.
If no volume control is available, at least support mute and full
volume switching if a playback switch exists.
This is also useful for being able to unmute S/PDIF devices.
Especially useful since there seem to be several driver/ALSA bugs
that mean these devices often start as muted after every boot.
---
 libao2/ao_alsa.c | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/libao2/ao_alsa.c b/libao2/ao_alsa.c
index 091bd00..2ec96f4 100644
--- a/libao2/ao_alsa.c
+++ b/libao2/ao_alsa.c
@@ -169,13 +169,50 @@ static int control(int cmd, void *arg)
       }
 
       elem = snd_mixer_find_selem(handle, sid);
+      if (!elem && !mixer_channel) {
+        // if nothing specified just try picking the first
+        elem = snd_mixer_first_elem(handle);
+        if (elem)
+            mp_msg(MSGT_AO, MSGL_V, "[AO_ALSA] Auto-selected element %s\n", snd_mixer_selem_get_name(elem));
+      }
       if (!elem) {
 	mp_msg(MSGT_AO,MSGL_ERR,MSGTR_AO_ALSA_UnableToFindSimpleControl,
 	       snd_mixer_selem_id_get_name(sid), snd_mixer_selem_id_get_index(sid));
+        mp_msg(MSGT_AO, MSGL_INFO, "[AO_ALSA] Available elements for device:\n");
+        for (elem = snd_mixer_first_elem(handle); elem; elem = snd_mixer_elem_next(elem))
+            mp_msg(MSGT_AO, MSGL_INFO, "[AO_ALSA]  %s\n", snd_mixer_selem_get_name(elem));
+        mp_msg(MSGT_AO, MSGL_INFO, "\n");
 	snd_mixer_close(handle);
 	return CONTROL_ERROR;
 	}
 
+      if (!snd_mixer_selem_has_playback_volume(elem) &&
+          !snd_mixer_selem_has_playback_volume_joined(elem))
+      {
+          if (!snd_mixer_selem_has_playback_switch(elem))
+              return CONTROL_FALSE;
+          if (cmd == AOCONTROL_GET_VOLUME) {
+              int v;
+              snd_mixer_selem_get_playback_switch(elem, SND_MIXER_SCHN_FRONT_LEFT, &v);
+              vol->left = v ? 100 : 0;
+              snd_mixer_selem_get_playback_switch(elem, SND_MIXER_SCHN_FRONT_RIGHT, &v);
+              vol->right = v ? 100 : 0;
+              return CONTROL_TRUE;
+          }
+          // special case: only mute supported
+          if (vol->left != 0 && vol->left != 100 ||
+              vol->right != 0 && vol->right != 100)
+              return CONTROL_FALSE;
+          if (snd_mixer_selem_has_playback_switch_joined(elem)) {
+              if (vol->left != vol->right)
+                  return CONTROL_FALSE;
+          } else {
+              snd_mixer_selem_set_playback_switch(elem, SND_MIXER_SCHN_FRONT_RIGHT, vol->right != 0);
+          }
+          snd_mixer_selem_set_playback_switch(elem, SND_MIXER_SCHN_FRONT_LEFT, vol->left != 0);
+          return CONTROL_TRUE;
+      }
+
       snd_mixer_selem_get_playback_volume_range(elem,&pmin,&pmax);
       f_multi = (100 / (float)(pmax - pmin));
 
-- 
1.9.1