Bug 1575638 - Perform the hard-right panning on macbook pros in Gecko and not in cubeb. r=kinetik

Panning support in cubeb was removed in 8c3e32bd24

Differential Revision: https://phabricator.services.mozilla.com/D43058

--HG--
extra : moz-landing-system : lando

dom/media/GraphDriver.cpp

@@ -898,6 +898,18 @@ long AudioCallbackDriver::DataCallback(const AudioDataValue* aInputBuffer,
   GraphImpl()->NotifyOutputData(aOutputBuffer, static_cast<size_t>(aFrames),
                                 mSampleRate, mOutputChannels);
 
+#ifdef XP_MACOSX
+  // This only happens when the output is on a macbookpro's external speaker,
+  // that are stereo, but let's just be safe.
+  if (mNeedsPanning && mOutputChannels == 2) {
+    // hard pan to the right
+    for (uint32_t i = 0; i < aFrames * 2; i += 2) {
+      aOutputBuffer[i + 1] += aOutputBuffer[i];
+      aOutputBuffer[i] = 0.0;
+    }
+  }
+#endif
+
   if (!stillProcessing) {
     // About to hand over control of the graph.  Do not start a new driver if
     // StateCallback() receives an error for this stream while the main thread
@@ -1013,19 +1025,12 @@ void AudioCallbackDriver::PanOutputIfNeeded(bool aMicrophoneActive) {
       // Check if we are currently outputing sound on external speakers.
       if (!strcmp(out->output_name, "ispk")) {
         // Pan everything to the right speaker.
-        if (aMicrophoneActive) {
-          if (cubeb_stream_set_panning(mAudioStream, 1.0) != CUBEB_OK) {
-            NS_WARNING("Could not pan audio output to the right.");
-          }
-        } else {
-          if (cubeb_stream_set_panning(mAudioStream, 0.0) != CUBEB_OK) {
-            NS_WARNING("Could not pan audio output to the center.");
-          }
-        }
+        LOG(LogLevel::Debug, ("Using the built-in speakers, with%s audio input",
+                              aMicrophoneActive ? "" : "out"));
+        mNeedsPanning = aMicrophoneActive;
       } else {
-        if (cubeb_stream_set_panning(mAudioStream, 0.0) != CUBEB_OK) {
-          NS_WARNING("Could not pan audio output to the center.");
-        }
+        LOG(LogLevel::Debug, ("Using an external output device"));
+        mNeedsPanning = false;
       }
       cubeb_stream_device_destroy(mAudioStream, out);
     }

dom/media/GraphDriver.h

@@ -534,6 +534,12 @@ class AudioCallbackDriver : public GraphDriver,
   /* True if this driver was created from a driver created because of a previous
    * AudioCallbackDriver failure. */
   bool mFromFallback;
+#ifdef XP_MACOSX
+  /* When using the built-in speakers on macbook pro (13 and 15, all models),
+   * it's best to hard pan the audio on the right, to avoid feedback into the
+   * microphone that is located next to the left speaker.  */
+  bool mNeedsPanning;
+#endif
 };
 
 class AsyncCubebTask : public Runnable {