introduce GetInOutLatencyMs to query the actual latency from the sound interface

src/client.cpp

@@ -1229,16 +1229,33 @@ int CClient::EstimatedOverallDelay ( const int iPingTimeMs )
         static_cast<double> ( GetSockBufNumFrames() +
                               GetServerSockBufNumFrames() ) / 2;
 
-    // we assume that we have two period sizes for the input and one for the
-    // output, therefore we have "3 *" instead of "2 *" (for input and output)
-    // the actual sound card buffer size, also consider delay introduced by
-    // sound card conversion buffer by using
-    // "GetSndCrdConvBufAdditionalDelayMonoBlSize"
-    const double dTotalSoundCardDelayMs =
-        ( 3 * GetSndCrdActualMonoBlSize() +
-        GetSndCrdConvBufAdditionalDelayMonoBlSize() ) *
+    // consider delay introduced by the sound card conversion buffer by using
+    // "GetSndCrdConvBufAdditionalDelayMonoBlSize()"
+    double dTotalSoundCardDelayMs = GetSndCrdConvBufAdditionalDelayMonoBlSize() *
         1000 / SYSTEM_SAMPLE_RATE_HZ;
 
+    // try to get the actual input/output sound card delay from the audio
+    // interface, per definition it is not available if a 0 is returned
+    const double dSoundCardInputOutputLatencyMs = Sound.GetInOutLatencyMs();
+
+    if ( dSoundCardInputOutputLatencyMs == 0.0 )
+    {
+        // use an alternative aproach for estimating the sound card delay:
+        //
+        // we assume that we have two period sizes for the input and one for the
+        // output, therefore we have "3 *" instead of "2 *" (for input and output)
+        // the actual sound card buffer size
+        // "GetSndCrdConvBufAdditionalDelayMonoBlSize"
+        dTotalSoundCardDelayMs +=
+            ( 3 * GetSndCrdActualMonoBlSize() ) *
+            1000 / SYSTEM_SAMPLE_RATE_HZ;
+    }
+    else
+    {
+        // add the actual sound card latency in ms
+        dTotalSoundCardDelayMs += dSoundCardInputOutputLatencyMs;
+    }
+
     // network packets are of the same size as the audio packets per definition
     // if no sound card conversion buffer is used
     const double dDelayToFillNetworkPacketsMs =

src/soundbase.h

@@ -77,6 +77,8 @@ public:
     virtual int     GetLeftOutputChannel()  { return 0; }
     virtual int     GetRightOutputChannel() { return 1; }
 
+    virtual double  GetInOutLatencyMs() { return 0.0; } // "0.0" means no latency is available
+
     virtual void    OpenDriverSetup() {}
 
     bool IsRunning() const { return bRun; }

windows/sound.cpp

@@ -363,6 +363,24 @@ int CSound::Init ( const int iNewPrefMonoBufferSize )
             2 /* in/out */ * NUM_IN_OUT_CHANNELS /* stereo */,
             iASIOBufferSizeMono, &asioCallbacks );
 
+        // query the latency of the driver
+        long lInputLatency  = 0;
+        long lOutputLatency = 0;
+
+        if ( ASIOGetLatencies ( &lInputLatency, &lOutputLatency ) != ASE_NotPresent )
+        {
+            // add the input and output latencies (returned in number of
+            // samples) and calculate the time in ms
+            dInOutLatencyMs =
+                ( static_cast<double> ( lInputLatency ) + lOutputLatency ) /
+                SYSTEM_SAMPLE_RATE_HZ * 1000;
+        }
+        else
+        {
+            // no latency available
+            dInOutLatencyMs = 0.0;
+        }
+
         // check wether the driver requires the ASIOOutputReady() optimization
         // (can be used by the driver to reduce output latency by one block)
         bASIOPostOutput = ( ASIOOutputReady() == ASE_OK );
@@ -402,7 +420,8 @@ CSound::CSound ( void (*fpNewCallback) ( CVector<int16_t>& psData, void* arg ),
     vSelectedInputChannels  ( NUM_IN_OUT_CHANNELS ),
     vSelectedOutputChannels ( NUM_IN_OUT_CHANNELS ),
     lNumInChan              ( 0 ),
-    lNumOutChan             ( 0 )
+    lNumOutChan             ( 0 ),
+    dInOutLatencyMs         ( 0.0 ) // "0.0" means that no latency value is available
 {
     int i;
 

windows/sound.h

@@ -72,6 +72,8 @@ public:
     virtual int     GetLeftOutputChannel()  { return vSelectedOutputChannels[0]; }
     virtual int     GetRightOutputChannel() { return vSelectedOutputChannels[1]; }
 
+    virtual double  GetInOutLatencyMs() { return dInOutLatencyMs; }
+
 protected:
     virtual QString  LoadAndInitializeDriver ( int iIdx );
     virtual void     UnloadCurrentDriver();
@@ -85,6 +87,7 @@ protected:
 
     long             lNumInChan;
     long             lNumOutChan;
+    double           dInOutLatencyMs;
     CVector<int>     vSelectedInputChannels;
     CVector<int>     vSelectedOutputChannels;