From 4bd993b1e3e8c5ae40fb9639dd9668321aa95abb Mon Sep 17 00:00:00 2001
From: Roman Lebedev <lebedev.ri@gmail.com>
Date: Sun, 9 Jul 2023 22:29:08 +0300
Subject: [PATCH] GstEngine/GstEnginePipeline: support gap-less playback w/
 loudness-normalizing gain

Ok, it does appear that it is that simple.

In principle this (even the non-update case) results in volume jumps,
so maybe we'll want gradual gain change...

Notably, i thought we'd always seek if the pipeline
was already operating on the same URL as the new one,
but apparently only for adjacent songs?
---
 src/engine/gstengine.cpp         |  4 ++--
 src/engine/gstenginepipeline.cpp | 21 ++++++++++++++++++---
 src/engine/gstenginepipeline.h   |  2 ++
 3 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/src/engine/gstengine.cpp b/src/engine/gstengine.cpp
index 813c0172..f84e38b9 100644
--- a/src/engine/gstengine.cpp
+++ b/src/engine/gstengine.cpp
@@ -190,9 +190,9 @@ bool GstEngine::Load(const QUrl &media_url, const QUrl &stream_url, const Engine
     crossfade = false;
   }
 
-  if (!crossfade && current_pipeline_ && current_pipeline_->stream_url() == stream_url && current_pipeline_->ebur128_loudness_normalizing_gain_db() == ebur128_loudness_normalizing_gain_db_ && change & EngineBase::TrackChangeType::Auto) {
+  if (!crossfade && current_pipeline_ && current_pipeline_->stream_url() == stream_url && change & EngineBase::TrackChangeType::Auto) {
     // We're not crossfading, and the pipeline is already playing the URI we want, so just do nothing.
-    // FIXME: can we handle changing of loudness-normalizing gain here?
+    current_pipeline_->SetEBUR128LoudnessNormalizingGain_dB(ebur128_loudness_normalizing_gain_db_);
     return true;
   }
 
diff --git a/src/engine/gstenginepipeline.cpp b/src/engine/gstenginepipeline.cpp
index b703be8f..117f4216 100644
--- a/src/engine/gstenginepipeline.cpp
+++ b/src/engine/gstenginepipeline.cpp
@@ -602,9 +602,7 @@ bool GstEnginePipeline::InitAudioBin(QString &error) {
       return false;
     }
 
-    auto dB_to_mult = [](const double gain_dB) { return std::pow(10., gain_dB / 20.); };
-
-    g_object_set(G_OBJECT(ebur128_volume_), "volume", dB_to_mult(ebur128_loudness_normalizing_gain_db_), nullptr);
+    UpdateEBUR128LoudnessNormalizingGaindB();
 
     eventprobe_ = ebur128_volume_;
   }
@@ -1535,6 +1533,23 @@ bool GstEnginePipeline::Seek(const qint64 nanosec) {
 
 }
 
+void GstEnginePipeline::SetEBUR128LoudnessNormalizingGain_dB(const double ebur128_loudness_normalizing_gain_db) {
+
+  ebur128_loudness_normalizing_gain_db_ = ebur128_loudness_normalizing_gain_db;
+  UpdateEBUR128LoudnessNormalizingGaindB();
+
+}
+
+void GstEnginePipeline::UpdateEBUR128LoudnessNormalizingGaindB() {
+
+  if (ebur128_volume_) {
+    auto dB_to_mult = [](const double gain_dB) { return std::pow(10., gain_dB / 20.); };
+
+    g_object_set(G_OBJECT(ebur128_volume_), "volume", dB_to_mult(ebur128_loudness_normalizing_gain_db_), nullptr);
+  }
+
+}
+
 void GstEnginePipeline::SetVolume(const uint volume_percent) {
 
   if (volume_) {
diff --git a/src/engine/gstenginepipeline.h b/src/engine/gstenginepipeline.h
index fc04e832..b670b7dc 100644
--- a/src/engine/gstenginepipeline.h
+++ b/src/engine/gstenginepipeline.h
@@ -87,6 +87,7 @@ class GstEnginePipeline : public QObject {
   // Control the music playback
   QFuture<GstStateChangeReturn> SetState(const GstState state);
   Q_INVOKABLE bool Seek(const qint64 nanosec);
+  void SetEBUR128LoudnessNormalizingGain_dB(const double ebur128_loudness_normalizing_gain_db);
   void SetVolume(const uint volume_percent);
   void SetStereoBalance(const float value);
   void SetEqualizerParams(const int preamp, const QList<int> &band_gains);
@@ -175,6 +176,7 @@ class GstEnginePipeline : public QObject {
   static QString ParseStrTag(GstTagList *list, const char *tag);
   static guint ParseUIntTag(GstTagList *list, const char *tag);
 
+  void UpdateEBUR128LoudnessNormalizingGaindB();
   void UpdateStereoBalance();
   void UpdateEqualizer();