Audio pitch changes on enabling / disabling the mic capture

https://bugs.webkit.org/show_bug.cgi?id=243651
rdar://problem/98655838

Reviewed by Eric Carlson.

When starting microphone capture, we stop the track remote IO unit and use the VPIO unit.
Previously we were stopping the remote IO unit when asking the VPIO unit to start.
The VPIO unit may take some time to start and audio to be rendered will start to be buffered.
We are getting rid of this buffering by speeding up a bit playback, leading to higher pitch.

To prevent this buffering, we are no longer stopping the remote IO unit when starting the VPIO unit.
Instead, we wait for the first speaker callback to ask the remote IO unit to stop after hopping to main thread.

* Source/WebCore/platform/mediastream/mac/BaseAudioSharedUnit.h:
* Source/WebCore/platform/mediastream/mac/CoreAudioSharedUnit.cpp:
(WebCore::CoreAudioSharedUnit::provideSpeakerData):
(WebCore::CoreAudioSharedUnit::startInternal):
* Source/WebCore/platform/mediastream/mac/CoreAudioSharedUnit.h:

Canonical link: https://commits.webkit.org/253673@main

Source/WebCore/platform/mediastream/mac/BaseAudioSharedUnit.h

@@ -42,7 +42,7 @@ class CaptureDevice;
 class CoreAudioCaptureSource;
 class PlatformAudioData;
 
-class BaseAudioSharedUnit : public CanMakeWeakPtr<BaseAudioSharedUnit> {
+class BaseAudioSharedUnit : public CanMakeWeakPtr<BaseAudioSharedUnit, WeakPtrFactoryInitialization::Eager> {
 public:
     BaseAudioSharedUnit();
     virtual ~BaseAudioSharedUnit() = default;

Source/WebCore/platform/mediastream/mac/CoreAudioSharedUnit.cpp

@@ -391,7 +391,19 @@ void CoreAudioSharedUnit::checkTimestamps(const AudioTimeStamp& timeStamp, doubl
 
 OSStatus CoreAudioSharedUnit::provideSpeakerData(AudioUnitRenderActionFlags& flags, const AudioTimeStamp& timeStamp, UInt32 /*inBusNumber*/, UInt32 inNumberFrames, AudioBufferList& ioData)
 {
-    if (m_isReconfiguring || !m_speakerSamplesProducerLock.tryLock()) {
+    if (m_isReconfiguring || m_shouldNotifySpeakerSamplesProducer || !m_hasNotifiedSpeakerSamplesProducer || !m_speakerSamplesProducerLock.tryLock()) {
+        if (m_shouldNotifySpeakerSamplesProducer) {
+            m_shouldNotifySpeakerSamplesProducer = false;
+            callOnMainThread([this, weakThis = WeakPtr { *this }] {
+                if (!weakThis)
+                    return;
+                m_hasNotifiedSpeakerSamplesProducer = true;
+                Locker locker { m_speakerSamplesProducerLock };
+                if (m_speakerSamplesProducer)
+                    m_speakerSamplesProducer->captureUnitIsStarting();
+            });
+        }
+
         AudioSampleBufferList::zeroABL(ioData, static_cast<size_t>(inNumberFrames * m_speakerProcFormat.bytesPerFrame()));
         flags = kAudioUnitRenderAction_OutputIsSilence;
         return noErr;
@@ -528,11 +540,8 @@ OSStatus CoreAudioSharedUnit::startInternal()
 
     unduck();
 
-    {
-        Locker locker { m_speakerSamplesProducerLock };
-        if (m_speakerSamplesProducer)
-            m_speakerSamplesProducer->captureUnitIsStarting();
-    }
+    m_shouldNotifySpeakerSamplesProducer = true;
+    m_hasNotifiedSpeakerSamplesProducer = false;
 
     if (auto err = m_ioUnit->start()) {
         {

Source/WebCore/platform/mediastream/mac/CoreAudioSharedUnit.h

@@ -147,6 +147,8 @@ class CoreAudioSharedUnit final : public BaseAudioSharedUnit {
 
     bool m_shouldUpdateMicrophoneSampleBufferSize { false };
     bool m_isReconfiguring { false };
+    bool m_shouldNotifySpeakerSamplesProducer { false };
+    bool m_hasNotifiedSpeakerSamplesProducer { false };
     mutable Lock m_speakerSamplesProducerLock;
     CoreAudioSpeakerSamplesProducer* m_speakerSamplesProducer WTF_GUARDED_BY_LOCK(m_speakerSamplesProducerLock) { nullptr };
 };