Fill sidechainMix from external sidechain input. This fixes lp1876222

src/engine/enginemaster.cpp

@@ -153,7 +153,9 @@ EngineMaster::EngineMaster(UserSettingsPointer pConfig,
     }
 
     // Starts a thread for recording and broadcast
-    m_pEngineSideChain = bEnableSidechain ? new EngineSideChain(pConfig) : NULL;
+    m_pEngineSideChain =
+            bEnableSidechain ?
+                    new EngineSideChain(pConfig, m_pSidechainMix) : nullptr;
 
     // X-Fader Setup
     m_pXFaderMode = new ControlPushButton(
@@ -632,7 +634,8 @@ void EngineMaster::process(const int iBufferSize) {
             SampleUtil::applyRampingGain(m_pMaster, m_masterGainOld,
                                          master_gain, m_iBufferSize);
             m_masterGainOld = master_gain;
-            if (!m_bExternalRecordBroadcastInputConnected) {
+            if (m_pEngineSideChain &&
+                    !m_bExternalRecordBroadcastInputConnected) {
                 SampleUtil::copy(m_pSidechainMix, m_pMaster, m_iBufferSize);
             }
 
@@ -651,8 +654,9 @@ void EngineMaster::process(const int iBufferSize) {
             // mixing the talkover signal for the record/broadcast mix.
             // If not using microphone inputs or recording/broadcasting from
             // a sound card input, skip unnecessary processing here.
-            if (m_pNumMicsConfigured->get() > 0
-                && !m_bExternalRecordBroadcastInputConnected) {
+            if (m_pEngineSideChain &&
+                    !m_bExternalRecordBroadcastInputConnected &&
+                    m_pNumMicsConfigured->get() > 0) {
                 // Copy the master mix to a separate buffer before delaying it
                 // to avoid delaying the master output.
                 m_pLatencyCompensationDelay->process(m_pSidechainMix, m_iBufferSize);
@@ -665,8 +669,7 @@ void EngineMaster::process(const int iBufferSize) {
         // If recording/broadcasting from a sound card input,
         // SoundManager will send the input buffer from the sound card to m_pSidechain
         // so skip sending a buffer to m_pSidechain here.
-        if (!m_bExternalRecordBroadcastInputConnected
-            && m_pEngineSideChain != nullptr) {
+        if (m_pEngineSideChain) {
             m_pEngineSideChain->writeSamples(m_pSidechainMix, iFrames);
         }
 

src/engine/sidechain/enginesidechain.cpp

@@ -28,6 +28,7 @@
 #include <QMutexLocker>
 
 #include "engine/sidechain/sidechainworker.h"
+#include "engine/engine.h"
 #include "util/counter.h"
 #include "util/event.h"
 #include "util/sample.h"
@@ -36,11 +37,14 @@
 
 #define SIDECHAIN_BUFFER_SIZE 65536
 
-EngineSideChain::EngineSideChain(UserSettingsPointer pConfig)
+EngineSideChain::EngineSideChain(
+        UserSettingsPointer pConfig,
+        CSAMPLE* sidechainMix)
         : m_pConfig(pConfig),
           m_bStopThread(false),
           m_sampleFifo(SIDECHAIN_BUFFER_SIZE),
-          m_pWorkBuffer(SampleUtil::alloc(SIDECHAIN_BUFFER_SIZE)) {
+          m_pWorkBuffer(SampleUtil::alloc(SIDECHAIN_BUFFER_SIZE)),
+          m_pSidechainMix(sidechainMix) {
     // We use HighPriority to prevent starvation by lower-priority processes (Qt
     // main thread, analysis, etc.). This used to be LowPriority but that is not
     // a suitable choice since we do semi-realtime tasks
@@ -78,11 +82,11 @@ void EngineSideChain::addSideChainWorker(SideChainWorker* pWorker) {
 void EngineSideChain::receiveBuffer(AudioInput input,
                                     const CSAMPLE* pBuffer,
                                     unsigned int iFrames) {
-    if (input.getType() != AudioInput::RECORD_BROADCAST) {
+    VERIFY_OR_DEBUG_ASSERT(input.getType() == AudioInput::RECORD_BROADCAST) {
         qDebug() << "WARNING: AudioInput type is not RECORD_BROADCAST. Ignoring incoming buffer.";
         return;
     }
-    writeSamples(pBuffer, iFrames);
+    SampleUtil::copy(m_pSidechainMix, pBuffer, iFrames * mixxx::kEngineChannelCount);
 }
 
 void EngineSideChain::writeSamples(const CSAMPLE* pBuffer, int iFrames) {

src/engine/sidechain/enginesidechain.h

@@ -32,7 +32,7 @@
 class EngineSideChain : public QThread, public AudioDestination {
     Q_OBJECT
   public:
-    EngineSideChain(UserSettingsPointer pConfig);
+    EngineSideChain(UserSettingsPointer pConfig, CSAMPLE* sidechainMix);
     virtual ~EngineSideChain();
 
     // Not thread-safe, wait-free. Submit buffer of samples to the sidechain for
@@ -58,6 +58,7 @@ class EngineSideChain : public QThread, public AudioDestination {
 
     FIFO<CSAMPLE> m_sampleFifo;
     CSAMPLE* m_pWorkBuffer;
+    CSAMPLE* m_pSidechainMix;
 
     // Provides thread safety around the wait condition below.
     QMutex m_waitLock;