Fill sidechainMix from external sidechain input. This fixes lp1876222

CHANGELOG

@@ -17,6 +17,7 @@
 * Add controller mapping for Hercules DJControl Inpulse 300 #2465
 * Add controller mapping for Denon MC7000 #2546
 * Add controller mapping for Stanton DJC.4 #2607
+* Fix broadcasting via broadcast/recording input lp:1876222 #2743
 
 ==== 2.2.3 2019-11-24 ====
 * Don't make users reconfigure sound hardware when it has not changed #2253

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(
@@ -562,7 +564,7 @@ void EngineMaster::process(const int iBufferSize) {
             m_masterGainOld = master_gain;
 
             // Record/broadcast signal is the same as the master output
-            if (!m_bExternalRecordBroadcastInputConnected) {
+            if (sidechainMixRequired()) {
                 SampleUtil::copy(m_pSidechainMix, m_pMaster, m_iBufferSize);
             }
         } else if (configuredMicMonitorMode == MicMonitorMode::MASTER_AND_BOOTH) {
@@ -599,7 +601,7 @@ void EngineMaster::process(const int iBufferSize) {
             m_masterGainOld = master_gain;
 
             // Record/broadcast signal is the same as the master output
-            if (!m_bExternalRecordBroadcastInputConnected) {
+            if (sidechainMixRequired()) {
                 SampleUtil::copy(m_pSidechainMix, m_pMaster, m_iBufferSize);
             }
         } else if (configuredMicMonitorMode == MicMonitorMode::DIRECT_MONITOR) {
@@ -632,41 +634,42 @@ void EngineMaster::process(const int iBufferSize) {
             SampleUtil::applyRampingGain(m_pMaster, m_masterGainOld,
                                          master_gain, m_iBufferSize);
             m_masterGainOld = master_gain;
-            if (!m_bExternalRecordBroadcastInputConnected) {
+            if (sidechainMixRequired()) {
                 SampleUtil::copy(m_pSidechainMix, m_pMaster, m_iBufferSize);
-            }
 
-            // The talkover signal Mixxx receives is delayed by the round trip latency.
-            // There is an output latency between the time Mixxx processes the audio
-            // and the user hears it. So if the microphone user plays on beat with
-            // what they hear, they will be playing out of sync with the engine's
-            // processing by the output latency. Additionally, Mixxx gets input signals
-            // delayed by the input latency. By the time Mixxx receives the input signal,
-            // a full round trip through the signal chain has elapsed since Mixxx
-            // processed the output signal.
-            // Although Mixxx receives the input signal delayed, the user hears it mixed
-            // in hardware with the master & booth outputs without that
-            // latency, so to record/broadcast the same signal that is heard
-            // on the master & booth outputs, the master mix must be delayed before
-            // 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) {
-                // Copy the master mix to a separate buffer before delaying it
-                // to avoid delaying the master output.
-                m_pLatencyCompensationDelay->process(m_pSidechainMix, m_iBufferSize);
-                SampleUtil::add(m_pSidechainMix, m_pTalkover, m_iBufferSize);
+                if (m_pNumMicsConfigured->get() > 0) {
+                    // The talkover signal Mixxx receives is delayed by the round trip latency.
+                    // There is an output latency between the time Mixxx processes the audio
+                    // and the user hears it. So if the microphone user plays on beat with
+                    // what they hear, they will be playing out of sync with the engine's
+                    // processing by the output latency. Additionally, Mixxx gets input signals
+                    // delayed by the input latency. By the time Mixxx receives the input signal,
+                    // a full round trip through the signal chain has elapsed since Mixxx
+                    // processed the output signal.
+                    // Although Mixxx receives the input signal delayed, the user hears it mixed
+                    // in hardware with the master & booth outputs without that
+                    // latency, so to record/broadcast the same signal that is heard
+                    // on the master & booth outputs, the master mix must be delayed before
+                    // 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.
+
+                    // Copy the master mix to a separate buffer before delaying it
+                    // to avoid delaying the master output.
+                    m_pLatencyCompensationDelay->process(m_pSidechainMix, m_iBufferSize);
+                    SampleUtil::add(m_pSidechainMix, m_pTalkover, m_iBufferSize);
+                }
             }
         }
 
-        // Submit buffer to the side chain to do broadcasting, recording,
-        // etc. (CPU intensive non-realtime tasks)
-        // 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) {
+        // Submit buffer to the side chain to do CPU intensive non-realtime
+        // tasks like recording. The SoundDeviceNetwork, responsible for
+        // passing samples to the network reads directly from m_pSidechainMix,
+        // registering it with SoundDevice::addOutput().
+        // Note: In case the broadcast/recording input is configured,
+        // EngineSideChain::receiveBuffer has copied the input buffer to m_pSidechainMix
+        // via before (called by SoundManager::pushInputBuffers())
+        if (m_pEngineSideChain) {
             m_pEngineSideChain->writeSamples(m_pSidechainMix, iFrames);
         }
 
@@ -963,3 +966,7 @@ void EngineMaster::registerNonEngineChannelSoundIO(SoundManager* pSoundManager)
     }
     pSoundManager->registerOutput(AudioOutput(AudioOutput::RECORD_BROADCAST, 0, 2), this);
 }
+
+bool EngineMaster::sidechainMixRequired() const {
+    return m_pEngineSideChain && !m_bExternalRecordBroadcastInputConnected;
+}

src/engine/enginemaster.h

@@ -273,6 +273,7 @@ class EngineMaster : public QObject, public AudioSource {
     ChannelHandleFactory* m_pChannelHandleFactory;
     void applyMasterEffects();
     void processHeadphones(const double masterMixGainInHeadphones);
+    bool sidechainMixRequired() const;
 
     EngineEffectsManager* m_pEngineEffectsManager;
 

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 +82,13 @@ 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);
+    // Just copy the received samples form the sound card input to the
+    // engine. After processing we get it back via writeSamples()
+    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;