feat(tracker): add menu item to export .wav

Also refactor the common functions for .wav export into base package so that both sointu-play and tracker can use same functions.

audioexport.go

@@ -0,0 +1,101 @@
+package sointu
+
+import (
+	"bytes"
+	"encoding/binary"
+	"fmt"
+	"math"
+)
+
+func Wav(buffer []float32, pcm16 bool) ([]byte, error) {
+	buf := new(bytes.Buffer)
+	wavHeader(len(buffer), pcm16, buf)
+	err := rawToBuffer(buffer, pcm16, buf)
+	if err != nil {
+		return nil, fmt.Errorf("Wav failed: %v", err)
+	}
+	return buf.Bytes(), nil
+}
+
+func Raw(buffer []float32, pcm16 bool) ([]byte, error) {
+	buf := new(bytes.Buffer)
+	err := rawToBuffer(buffer, pcm16, buf)
+	if err != nil {
+		return nil, fmt.Errorf("Raw failed: %v", err)
+	}
+	return buf.Bytes(), nil
+}
+
+func rawToBuffer(data []float32, pcm16 bool, buf *bytes.Buffer) error {
+	var err error
+	if pcm16 {
+		int16data := make([]int16, len(data))
+		for i, v := range data {
+			int16data[i] = int16(clamp(int(v*math.MaxInt16), math.MinInt16, math.MaxInt16))
+		}
+		err = binary.Write(buf, binary.LittleEndian, int16data)
+	} else {
+		err = binary.Write(buf, binary.LittleEndian, data)
+	}
+	if err != nil {
+		return fmt.Errorf("could not binary write data to binary buffer: %v", err)
+	}
+	return nil
+}
+
+// wavHeader writes a wave header for either float32 or int16 .wav file into the
+// bytes.buffer. It needs to know the length of the buffer and assumes stereo
+// sound, so the length in stereo samples (L + R) is bufferlength / 2. If pcm16
+// = true, then the header is for int16 audio; pcm16 = false means the header is
+// for float32 audio. Assumes 44100 Hz sample rate.
+func wavHeader(bufferLength int, pcm16 bool, buf *bytes.Buffer) {
+	// Refer to: http://www-mmsp.ece.mcgill.ca/Documents/AudioFormats/WAVE/WAVE.html
+	numChannels := 2
+	sampleRate := 44100
+	var bytesPerSample, chunkSize, fmtChunkSize, waveFormat int
+	var factChunk bool
+	if pcm16 {
+		bytesPerSample = 2
+		chunkSize = 36 + bytesPerSample*bufferLength
+		fmtChunkSize = 16
+		waveFormat = 1 // PCM
+		factChunk = false
+	} else {
+		bytesPerSample = 4
+		chunkSize = 50 + bytesPerSample*bufferLength
+		fmtChunkSize = 18
+		waveFormat = 3 // IEEE float
+		factChunk = true
+	}
+	buf.Write([]byte("RIFF"))
+	binary.Write(buf, binary.LittleEndian, uint32(chunkSize))
+	buf.Write([]byte("WAVE"))
+	buf.Write([]byte("fmt "))
+	binary.Write(buf, binary.LittleEndian, uint32(fmtChunkSize))
+	binary.Write(buf, binary.LittleEndian, uint16(waveFormat))
+	binary.Write(buf, binary.LittleEndian, uint16(numChannels))
+	binary.Write(buf, binary.LittleEndian, uint32(sampleRate))
+	binary.Write(buf, binary.LittleEndian, uint32(sampleRate*numChannels*bytesPerSample)) // avgBytesPerSec
+	binary.Write(buf, binary.LittleEndian, uint16(numChannels*bytesPerSample))            // blockAlign
+	binary.Write(buf, binary.LittleEndian, uint16(8*bytesPerSample))                      // bits per sample
+	if fmtChunkSize > 16 {
+		binary.Write(buf, binary.LittleEndian, uint16(0)) // size of extension
+	}
+	if factChunk {
+		buf.Write([]byte("fact"))
+		binary.Write(buf, binary.LittleEndian, uint32(4))            // fact chunk size
+		binary.Write(buf, binary.LittleEndian, uint32(bufferLength)) // sample length
+	}
+	buf.Write([]byte("data"))
+	binary.Write(buf, binary.LittleEndian, uint32(bytesPerSample*bufferLength))
+}
+
+func clamp(value, min, max int) int {
+	if value < min {
+		return min
+	}
+	if value > max {
+		return max
+	}
+	return value
+}