the most basic, generally not-correct linear interpolating resampling filter

examples/src/Main.cpp

@@ -40,8 +40,8 @@ int main(int argc, const char **argv) try
         // 1-channel wave
         //loader.Load(fileData.get(), "test_data/1ch/44100/8/test.wav");
         //loader.Load(fileData.get(), "test_data/1ch/44100/16/test.wav");
-        //loader.Load(fileData.get(), "test_data/1ch/44100/24/test.wav");
-        loader.Load(fileData.get(), "test_data/1ch/44100/32/test.wav");
+        loader.Load(fileData.get(), "test_data/1ch/44100/24/test.wav");
+        //loader.Load(fileData.get(), "test_data/1ch/44100/32/test.wav");
         //loader.Load(fileData.get(), "test_data/1ch/44100/64/test.wav");
 
         // 2-channel wave
@@ -104,6 +104,13 @@ int main(int argc, const char **argv) try
 		std::cout << "[Warning - Sample Rate Mismatch] - file is sampled at " << fileData->sampleRate << " and output is " << desiredSampleRate << std::endl;
 	}
 
+	std::vector<float> outputBuffer;
+	outputBuffer.reserve(fileData->samples.size());
+	linear_resample(44100.0 / 48000.0, fileData->samples, outputBuffer, fileData->samples.size());
+
+	std::cout << "Input Samples: " << fileData->samples.size() << std::endl;
+	std::cout << "Output Samples: " << outputBuffer.size() << std::endl;
+
 	// Convert mono to stereo for testing playback
 	if (fileData->channelCount == 1)
 	{
@@ -118,6 +125,7 @@ int main(int argc, const char **argv) try
 		myDevice.Play(fileData->samples);
 	}
 
+	fileData->samples = outputBuffer;
 	int encoderStatus = OggOpusEncoder::WriteFile({1, PCM_FLT, DITHER_NONE}, fileData.get(), "encoded.opus");
     std::cout << "Encoder Status: " << encoderStatus << std::endl;
  

include/libnyquist/WavEncoder.h

@@ -33,32 +33,55 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 namespace nqr
 {
 
-enum EncoderError
-{
-    NoError,
-    InsufficientSampleData,
-    FileIOError,
-    UnsupportedSamplerate,
-    UnsupportedChannelConfiguration,
-    UnsupportedBitdepth,
-    UnsupportedChannelMix,
-    BufferTooBig,
-};
+	static inline void linear_resample(const double rate, const std::vector<float> & input, std::vector<float> & output, size_t samplesToProcess)
+	{
+		float * source = const_cast<float *>(input.data());
+
+		double virtualReadIndex = 0;
+
+		// Linear Interpolate
+		int n = samplesToProcess - 1;
+		while (n--)
+		{
+			unsigned readIndex = static_cast<unsigned>(virtualReadIndex);
+			double interpolationFactor = virtualReadIndex - readIndex;
+
+			double sample1 = source[readIndex];
+			double sample2 = source[readIndex + 1];
+
+			double sample = (1.0 - interpolationFactor) * sample1 + interpolationFactor * sample2;
+
+			output.push_back(sample);
+
+			virtualReadIndex += rate;
+		}
+	}
+
+	enum EncoderError
+	{
+		NoError,
+		InsufficientSampleData,
+		FileIOError,
+		UnsupportedSamplerate,
+		UnsupportedChannelConfiguration,
+		UnsupportedBitdepth,
+		UnsupportedChannelMix,
+		BufferTooBig,
+	};
     
+	// A simplistic encoder that takes a blob of data, conforms it to the user's
+	// EncoderParams preference, and writes to disk. Be warned, does not support resampling!
+	// @todo support dithering, samplerate conversion, etc.
+	struct WavEncoder
+	{
+		// Assume data adheres to EncoderParams, except for bit depth and fmt
+		static int WriteFile(const EncoderParams p, const AudioData * d, const std::string & path);
+	};
 
-// A simplistic encoder that takes a blob of data, conforms it to the user's
-// EncoderParams preference, and writes to disk. Be warned, does not support resampling!
-// @todo support dithering, samplerate conversion, etc.
-struct WavEncoder
-{
-    // Assume data adheres to EncoderParams, except for bit depth and fmt
-    static int WriteFile(const EncoderParams p, const AudioData * d, const std::string & path);
-};
-
-struct OggOpusEncoder
-{
-    static int WriteFile(const EncoderParams p, const AudioData * d, const std::string & path);
-};
+	struct OggOpusEncoder
+	{
+		static int WriteFile(const EncoderParams p, const AudioData * d, const std::string & path);
+	};
 
 } // end namespace nqr
 

src/WavEncoder.cpp

@@ -450,4 +450,4 @@ int OggOpusEncoder::WriteFile(const EncoderParams p, const AudioData * d, const
     return EncoderError::NoError;
 }
 
-#undef OPUS_MAX_PACKET_SIZE
+#undef OPUS_MAX_PACKET_SIZE