exporter: wait for conforms/indexes when exporting audio

The audio rendering system uses an event-based mechanism where if audio needs
to be converted (i.e. to a different sample rate), it will create a conform
task and re-render that section again when the audio is ready. Unfortunately,
the export code didn't respect this and would start encoding audio once the
initial queue was done. This usually resulted in silent audio, but could also
result in "uninitialized" audio that would crash any float-based encoders
(e.g. AAC). Now we use a different signal that only emits once the queue is done
AND all conforms are done.

app/render/backend/audiorenderbackend.cpp

@@ -12,6 +12,7 @@ AudioRenderBackend::AudioRenderBackend(QObject *parent) :
   ic_from_conform_(false)
 {
   connect(IndexManager::instance(), &IndexManager::StreamConformAppended, this, &AudioRenderBackend::ConformUpdated);
+  connect(this, &AudioRenderBackend::QueueComplete, this, &AudioRenderBackend::FilterQueueCompleteSignal);
 }
 
 void AudioRenderBackend::SetParameters(const AudioRenderingParams &params)
@@ -205,6 +206,13 @@ void AudioRenderBackend::TruncateCache(const rational &r)
   }
 }
 
+void AudioRenderBackend::FilterQueueCompleteSignal()
+{
+  if (conform_wait_info_.isEmpty()) {
+    emit AudioComplete();
+  }
+}
+
 bool AudioRenderBackend::ConformWaitInfo::operator==(const AudioRenderBackend::ConformWaitInfo &rhs) const
 {
   return rhs.params == params

app/render/backend/audiorenderbackend.h

@@ -27,6 +27,8 @@ public:
 signals:
   void ParamsChanged();
 
+  void AudioComplete();
+
 protected:
   virtual void ConnectViewer(ViewerOutput* node) override;
 
@@ -76,6 +78,8 @@ private slots:
 
   void TruncateCache(const rational& r);
 
+  void FilterQueueCompleteSignal();
+
 };
 
 #endif // AUDIORENDERBACKEND_H

app/render/backend/exporter.cpp

@@ -245,7 +245,7 @@ void Exporter::EncoderOpenedSuccessfully()
 
   if (!audio_done_) {
     // We set the audio backend to render the full sequence to the disk
-    connect(audio_backend_, &AudioRenderBackend::QueueComplete, this, &Exporter::AudioRendered);
+    connect(audio_backend_, &AudioRenderBackend::AudioComplete, this, &Exporter::AudioRendered);
 
     audio_backend_->InvalidateCache(TimeRange(0, viewer_node_->Length()));
   }