Improve jack audio engine latency

Listen to the jack server latency callback
Ableton · Jun 17, 2020 · f7432a4 · f7432a4
1 parent aba21b3
commit f7432a4
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Showing 2 changed files with 24 additions and 9 deletions.
diff --git a/examples/linkaudio/AudioPlatform_Jack.cpp b/examples/linkaudio/AudioPlatform_Jack.cpp
@@ -49,6 +49,20 @@ int AudioPlatform::audioCallback(jack_nframes_t nframes, void* pvUserData)
   return pAudioPlatform->audioCallback(nframes);
 }
 
+void AudioPlatform::latencyCallback(jack_latency_callback_mode_t, void* pvUserData)
+{
+  AudioPlatform* pAudioPlatform = static_cast<AudioPlatform*>(pvUserData);
+  pAudioPlatform->updateLatency();
+}
+
+void AudioPlatform::updateLatency()
+{
+  jack_latency_range_t latencyRange;
+  jack_port_get_latency_range(mpJackPorts[0], JackPlaybackLatency, &latencyRange);
+  mEngine.mOutputLatency.store(
+    std::chrono::microseconds(llround(1.0e6 * latencyRange.max / mEngine.mSampleRate)));
+}
+
 int AudioPlatform::audioCallback(jack_nframes_t nframes)
 {
   using namespace std::chrono;
@@ -106,7 +120,15 @@ void AudioPlatform::initialize()
     std::terminate();
   };
 
+  const double bufferSize = jack_get_buffer_size(mpJackClient);
+  const double sampleRate = jack_get_sample_rate(mpJackClient);
+  mEngine.setBufferSize(static_cast<std::size_t>(bufferSize));
+  mEngine.setSampleRate(sampleRate);
+
+  jack_set_latency_callback(mpJackClient, AudioPlatform::latencyCallback, this);
+
   mpJackPorts = new jack_port_t*[2];
+
   for (int k = 0; k < 2; ++k)
   {
     const std::string port_name = "out_" + std::to_string(k + 1);
@@ -121,15 +143,6 @@ void AudioPlatform::initialize()
   }
 
   jack_set_process_callback(mpJackClient, AudioPlatform::audioCallback, this);
-
-  const double bufferSize = jack_get_buffer_size(mpJackClient);
-  const double sampleRate = jack_get_sample_rate(mpJackClient);
-
-  mEngine.setBufferSize(static_cast<std::size_t>(bufferSize));
-  mEngine.setSampleRate(sampleRate);
-
-  mEngine.mOutputLatency =
-    std::chrono::microseconds(llround(1.0e6 * bufferSize / sampleRate));
 }
 
 void AudioPlatform::uninitialize()

diff --git a/examples/linkaudio/AudioPlatform_Jack.hpp b/examples/linkaudio/AudioPlatform_Jack.hpp
@@ -40,6 +40,8 @@ class AudioPlatform
 private:
   static int audioCallback(jack_nframes_t nframes, void* pvUserData);
   int audioCallback(jack_nframes_t nframes);
+  static void latencyCallback(jack_latency_callback_mode_t mode, void* pvUserData);
+  void updateLatency();
 
   void initialize();
   void uninitialize();