chore: initialize go-sip repository

internal/audio/pcm16.go

@@ -0,0 +1,35 @@
+// Package audio contains small, shared PCM16 transformations used by media and AI adapters.
+package audio
+
+import "encoding/binary"
+
+// ResamplePCM16 linearly resamples mono signed little-endian PCM16.
+// It preserves an empty input and returns a copy when the rates match.
+func ResamplePCM16(src []byte, sourceRate, targetRate int) []byte {
+	if sourceRate <= 0 || targetRate <= 0 || len(src) < 2 || sourceRate == targetRate {
+		return append([]byte(nil), src...)
+	}
+	samples := len(src) / 2
+	outSamples := samples * targetRate / sourceRate
+	if outSamples < 1 {
+		return nil
+	}
+	out := make([]byte, outSamples*2)
+	for i := 0; i < outSamples; i++ {
+		position := float64(i) * float64(sourceRate) / float64(targetRate)
+		left := int(position)
+		if left >= samples {
+			left = samples - 1
+		}
+		right := left + 1
+		if right >= samples {
+			right = left
+		}
+		frac := position - float64(left)
+		lv := int16(binary.LittleEndian.Uint16(src[left*2 : left*2+2]))
+		rv := int16(binary.LittleEndian.Uint16(src[right*2 : right*2+2]))
+		value := int16(float64(lv)*(1-frac) + float64(rv)*frac)
+		binary.LittleEndian.PutUint16(out[i*2:i*2+2], uint16(value))
+	}
+	return out
+}