From f8e693a060705faddbbebca77a059b33a5d923d6 Mon Sep 17 00:00:00 2001
From: Cameron Gutman <aicommander@gmail.com>
Date: Thu, 14 Feb 2019 22:32:54 -0800
Subject: [PATCH] Drop samples to account for lost time reinitializing audio.
 Fixes #176

---
 app/streaming/audio/audio.cpp | 27 +++++++++++++++++++++++++++
 app/streaming/session.cpp     |  3 ++-
 app/streaming/session.h       |  1 +
 3 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/app/streaming/audio/audio.cpp b/app/streaming/audio/audio.cpp
index c61312e2..e77d2d2b 100644
--- a/app/streaming/audio/audio.cpp
+++ b/app/streaming/audio/audio.cpp
@@ -115,6 +115,21 @@ void Session::arDecodeAndPlaySample(char* sampleData, int sampleLength)
         }
     }
 
+    // See if we need to drop this sample
+    if (s_ActiveSession->m_DropAudioEndTime != 0) {
+        if (SDL_TICKS_PASSED(SDL_GetTicks(), s_ActiveSession->m_DropAudioEndTime)) {
+            // Avoid calling SDL_GetTicks() now
+            s_ActiveSession->m_DropAudioEndTime = 0;
+
+            SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION,
+                        "Audio drop window has ended");
+        }
+        else {
+            // We're still in the drop window
+            return;
+        }
+    }
+
     s_ActiveSession->m_AudioSampleCount++;
 
     if (s_ActiveSession->m_AudioRenderer != nullptr) {
@@ -145,10 +160,22 @@ void Session::arDecodeAndPlaySample(char* sampleData, int sampleLength)
     // safe to reinitialize here because we can't be torn down while
     // the audio decoder/playback thread is still alive.
     if (s_ActiveSession->m_AudioRenderer == nullptr && (s_ActiveSession->m_AudioSampleCount % 200) == 0) {
+        // Since we're doing this inline and audio initialization takes time, we need
+        // to drop samples to account for the time we've spent blocking audio rendering
+        // so we return to real-time playback and don't accumulate latency.
+        Uint32 audioReinitStartTime = SDL_GetTicks();
+
         s_ActiveSession->m_AudioRenderer = s_ActiveSession->createAudioRenderer();
         if (!s_ActiveSession->m_AudioRenderer->prepareForPlayback(&s_ActiveSession->m_AudioConfig)) {
             delete s_ActiveSession->m_AudioRenderer;
             s_ActiveSession->m_AudioRenderer = nullptr;
         }
+
+        Uint32 audioReinitStopTime = SDL_GetTicks();
+
+        s_ActiveSession->m_DropAudioEndTime = audioReinitStopTime + (audioReinitStopTime - audioReinitStartTime);
+        SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION,
+                    "Audio reinitialization took %d ms - starting drop window",
+                    audioReinitStopTime - audioReinitStartTime);
     }
 }
diff --git a/app/streaming/session.cpp b/app/streaming/session.cpp
index 1cf661db..bdc91eb7 100644
--- a/app/streaming/session.cpp
+++ b/app/streaming/session.cpp
@@ -312,7 +312,8 @@ Session::Session(NvComputer* computer, NvApp& app, StreamingPreferences *prefere
       m_InputHandlerLock(0),
       m_OpusDecoder(nullptr),
       m_AudioRenderer(nullptr),
-      m_AudioSampleCount(0)
+      m_AudioSampleCount(0),
+      m_DropAudioEndTime(0)
 {
 }
 
diff --git a/app/streaming/session.h b/app/streaming/session.h
index 4b063ae2..d710f696 100644
--- a/app/streaming/session.h
+++ b/app/streaming/session.h
@@ -149,6 +149,7 @@ private:
     IAudioRenderer* m_AudioRenderer;
     OPUS_MULTISTREAM_CONFIGURATION m_AudioConfig;
     int m_AudioSampleCount;
+    Uint32 m_DropAudioEndTime;
 
     Overlay::OverlayManager m_OverlayManager;