Compensate initial buffering of anti-alias filter and intepolator.

This avoids losing first few dozen of samples from beginning of the stream.

Signed-off-by: Olli Parviainen <oparviai at iki.fi>

include/FIFOSampleBuffer.h

@@ -170,6 +170,9 @@ public:
     /// allow trimming (downwards) amount of samples in pipeline.
     /// Returns adjusted amount of samples
     uint adjustAmountOfSamples(uint numSamples);
+
+    /// Add silence to end of buffer
+    void addSilent(uint nSamples);
 };
 
 }

source/SoundTouch/FIFOSampleBuffer.cpp

@@ -265,3 +265,11 @@ uint FIFOSampleBuffer::adjustAmountOfSamples(uint numSamples)
     }
     return samplesInBuffer;
 }
+
+
+/// Add silence to end of buffer
+void FIFOSampleBuffer::addSilent(uint nSamples)
+{
+    memset(ptrEnd(nSamples), 0, sizeof(SAMPLETYPE) * nSamples * channels);
+    samplesInBuffer += nSamples;
+}

source/SoundTouch/InterpolateCubic.h

@@ -56,6 +56,11 @@ protected:
 
 public:
     InterpolateCubic();
+
+    int getLatency() const
+    {
+        return 1;
+    }
 };
 
 }

source/SoundTouch/InterpolateLinear.h

@@ -60,6 +60,11 @@ public:
     /// Sets new target rate. Normal rate = 1.0, smaller values represent slower 
     /// rate, larger faster rates.
     virtual void setRate(double newRate);
+
+    int getLatency() const
+    {
+        return 0;
+    }
 };
 
 
@@ -81,6 +86,11 @@ protected:
 
 public:
     InterpolateLinearFloat();
+
+    int getLatency() const
+    {
+        return 0;
+    }
 };
 
 }

source/SoundTouch/InterpolateShannon.h

@@ -61,6 +61,11 @@ protected:
 
 public:
     InterpolateShannon();
+
+    int getLatency() const
+    {
+        return 3;
+    }
 };
 
 }

source/SoundTouch/RateTransposer.cpp

@@ -61,6 +61,7 @@ RateTransposer::RateTransposer() : FIFOProcessor(&outputBuffer)
     // Instantiates the anti-alias filter
     pAAFilter = new AAFilter(64);
     pTransposer = TransposerBase::newInstance();
+    clear();
 }
 
 
@@ -192,6 +193,10 @@ void RateTransposer::clear()
     outputBuffer.clear();
     midBuffer.clear();
     inputBuffer.clear();
+
+    // prefill buffer to avoid losing first samples at beginning of stream
+    int prefill = getLatency();
+    inputBuffer.addSilent(prefill);
 }
 
 
@@ -209,7 +214,8 @@ int RateTransposer::isEmpty() const
 /// Return approximate initial input-output latency
 int RateTransposer::getLatency() const
 {
-    return (bUseAAFilter) ? pAAFilter->getLength() : 0;
+    return pTransposer->getLatency() +
+        ((bUseAAFilter) ? (pAAFilter->getLength() / 2) : 0);
 }
 
 

source/SoundTouch/RateTransposer.h

@@ -83,6 +83,7 @@ public:
     virtual int transpose(FIFOSampleBuffer &dest, FIFOSampleBuffer &src);
     virtual void setRate(double newRate);
     virtual void setChannels(int channels);
+    virtual int getLatency() const = 0;
 
     // static factory function
     static TransposerBase *newInstance();