Adds a platform independent detecion of microphone hardware mute

media/audio/audio_input_controller.cc

Index: media/audio/audio_input_controller.cc
diff --git a/media/audio/audio_input_controller.cc b/media/audio/audio_input_controller.cc
index c27e933c00fe407d0173c65c1e9cf80c91f07dc1..0b9bc0fc6ff383fdde1cf9df3c384b4c11f21e16 100644
--- a/media/audio/audio_input_controller.cc
+++ b/media/audio/audio_input_controller.cc
@@ -10,13 +10,28 @@
 #include "base/threading/thread_restrictions.h"
 #include "base/time/time.h"
 #include "media/audio/audio_parameters.h"
-#include "media/base/limits.h"
 #include "media/base/scoped_histogram_timer.h"
 #include "media/base/user_input_monitor.h"
 
 using base::TimeDelta;
 
 namespace {
+
+// Logs if the user has enabled the microphone mute or not. This is normally
+// done by marking a checkbox in an audio-settings UI which is unique for each
+// platform. Elements in this enum should not be added, deleted or rearranged.
+enum MicrophoneMuteResult {
+  MICROPHONE_IS_NOT_MUTED = 0,
+  MICROPHONE_IS_MUTED = 1,
+  MICROPHONE_MUTE_MAX = MICROPHONE_IS_NOT_MUTED

[tommi (sloooow) - chröme, 2014/09/19 13:09:32]

hmm... I think this should be MICROPHONE_IS_MUTED as is.  (max is actually 0)

However, do you mind switching this so that "IS_MUTED"  comes first?
basically:

IS_MUTED = 0,
IS_NOT_MUTED = 1,
MUTE_MAX = IS_NOT_MUTED

[henrika (OOO until Aug 14), 2014/09/19 14:57:43]

Done.

+};
+
+void LogMicrophoneMuteResult(MicrophoneMuteResult result) {
+  UMA_HISTOGRAM_ENUMERATION("Media.MicrophoneMuted",
+                            result,
+                            MICROPHONE_MUTE_MAX + 1);
+}
+
 const int kMaxInputChannels = 3;
 
 // TODO(henrika): remove usage of timers and add support for proper
@@ -577,6 +592,20 @@ void AudioInputController::DoLogAudioLevels(float level_dbfs,
   if (microphone_volume_percent < kLowLevelMicrophoneLevelPercent)
     log_string += " <=> low microphone level!";
   handler_->OnLog(this, log_string);
+
+  // Try to detect if the user has enabled hardware mute by pressing the mute
+  // button in audio settings for the selected microphone. The idea here is to

[tommi (sloooow) - chröme, 2014/09/19 13:09:32]

do you know if this is the equivalent of a hardware mute or if this is
implemented in software (possibly in kernel mode)?

The reason I'm wondering about this is because of microphones that actually have
a physical on/off button which the user can play around with which does not
affect the software state.  I think that the physical button scenario is what hw
mute detection was meant to detect (i.e. not related to audio settings).

Because of this, I think that the practical difference between software mute and
hardware mute could be that the former will deliver all zeros when muted, but
the hw solution might actually deliver non-zero samples when muted.

[henrika (OOO until Aug 14), 2014/09/19 14:57:42]

I tried one USB headset with mute button and when activating, the mute check box
was not marked. Audio was still recorded at a reasonable level but it was silent
in loopback. I was not able to restore audio again so something is broken with
this headset. Will try on other platforms next.

+  // detect when all input samples are zeros but the actual volume slider is
+  // larger than zero. It should correspond to a hardware mute state.
+  if (level_dbfs == -std::numeric_limits<float>::infinity() &&
+      microphone_volume_percent > 0) {
+    LogMicrophoneMuteResult(MICROPHONE_IS_MUTED);
+    log_string = base::StringPrintf(
+        "AIC::OnData: microphone is most likely hardware muted!");

[tommi (sloooow) - chröme, 2014/09/19 13:09:32]

nit: "microphone muted" is probably enough

[henrika (OOO until Aug 14), 2014/09/19 14:57:42]

Done.

+    handler_->OnLog(this, log_string);
+  } else {
+    LogMicrophoneMuteResult(MICROPHONE_IS_NOT_MUTED);
+  }
 #endif
 }