Mute ALSA audio completely

chrome/browser/chromeos/audio_mixer_alsa.cc

Index: chrome/browser/chromeos/audio_mixer_alsa.cc
diff --git a/chrome/browser/chromeos/audio_mixer_alsa.cc b/chrome/browser/chromeos/audio_mixer_alsa.cc
index 34fb722ab0e51b9ad098568e9949764a95a530d4..ca99065d4b093635bdd59826ab884a05eb3d59e6 100644
--- a/chrome/browser/chromeos/audio_mixer_alsa.cc
+++ b/chrome/browser/chromeos/audio_mixer_alsa.cc
@@ -175,8 +175,6 @@ void AudioMixerAlsa::SetMute(bool mute) {
   }
 
   SetElementMuted_Locked(elem_master_, mute);
-  if (elem_pcm_)
-    SetElementMuted_Locked(elem_pcm_, mute);

[davejcool, 2011/03/03 20:05:02]

It turns out the PCM mixer element does have a mute control and does not need to
be muted as well.  Before this change CL, the PCM element was not even being
found, so this was not noticed.

   prefs_->SetInteger(prefs::kAudioMute, mute ? kPrefMuteOn : kPrefMuteOff);
 }
 
@@ -246,6 +244,21 @@ bool AudioMixerAlsa::InitializeAlsaMixer() {
   snd_mixer_t* handle = NULL;
   const char* card = "default";
 
+  // Verify PCM can be opened, which also instantiates the PCM mixer element
+  // which is needed for finer volume control and for muting by setting to zero.
+  // If it fails, we can still try to use the mixer as best we can.
+  snd_pcm_t* pcm_out_handle;
+  if ((err = snd_pcm_open(&pcm_out_handle,
+                          "default",
+                          SND_PCM_STREAM_PLAYBACK,
+                          0)) >= 0) {
+    snd_pcm_close(pcm_out_handle);
+  }
+  else
+  {
+    LOG(WARNING) << "ALSA PCM open: " << snd_strerror(err);
+  }
+
   if ((err = snd_mixer_open(&handle, 0)) < 0) {
     LOG(ERROR) << "ALSA mixer " << card << " open error: " << snd_strerror(err);
     return false;
@@ -348,8 +361,6 @@ void AudioMixerAlsa::DoSetVolumeMute(double pref_volume, int pref_mute) {
   }
 
   SetElementMuted_Locked(elem_master_, mute);
-  if (elem_pcm_)
-    SetElementMuted_Locked(elem_pcm_, mute);
 }
 
 void AudioMixerAlsa::RestoreVolumeMuteOnUIThread() {