Bug 1023947 - Part 1 - Drop frame instead of buffering them when we are swiching device. r=jesup

--HG--
extra : rebase_source : 9e5f70c2c8aa9bc826e8bee561285da5220bf895

content/media/AudioStream.cpp

@@ -253,6 +253,7 @@ AudioStream::AudioStream()
   , mBytesPerFrame(0)
   , mState(INITIALIZED)
   , mNeedsStart(false)
+  , mShouldDropFrames(false)
 {
   // keep a ref in case we shut down later than nsLayoutStatics
   mLatencyLog = AsyncLatencyLogger::Get(true);
@@ -591,6 +592,7 @@ void AudioStream::PanOutputIfNeeded(bool aMicrophoneActive)
 void AudioStream::DeviceChangedCallback() {
   MonitorAutoLock mon(mMonitor);
   PanOutputIfNeeded(mMicrophoneActive);
+  mShouldDropFrames = true;
 }
 
 // This code used to live inside AudioStream::Init(), but on Mac (others?)
@@ -712,6 +714,10 @@ nsresult
 AudioStream::Write(const AudioDataValue* aBuf, uint32_t aFrames, TimeStamp *aTime)
 {
   MonitorAutoLock mon(mMonitor);
+  if (mShouldDropFrames) {
+    mBuffer.ContractTo(0);
+    return NS_OK;
+  }
   if (mState == ERRORED) {
     return NS_ERROR_FAILURE;
   }
@@ -1113,6 +1119,8 @@ AudioStream::DataCallback(void* aBuffer, long aFrames)
   uint32_t servicedFrames = 0;
   int64_t insertTime;
 
+  mShouldDropFrames = false;
+
   // NOTE: wasapi (others?) can call us back *after* stop()/Shutdown() (mState == SHUTDOWN)
   // Bug 996162
 

content/media/AudioStream.h

@@ -407,6 +407,10 @@ private:
   bool mIsFirst;
   // True if a microphone is active.
   bool mMicrophoneActive;
+  // When we are in the process of changing the output device, and the callback
+  // is not going to be called for a little while, simply drop incoming frames.
+  // This is only on OSX for now, because other systems handle this gracefully.
+  bool mShouldDropFrames;
 
   // This mutex protects the static members below.
   static StaticMutex sMutex;