chore: add Apache License 2.0 and ignore build directory

src/audio/audio.go

@@ -31,6 +31,10 @@ func DurationSamples(duration time.Duration) int {
 	return int(duration * SampleRate / time.Second)
 }
 
+func SamplesDuration(samples int) time.Duration {
+	return time.Duration(samples) * time.Second / SampleRate
+}
+
 func RMSDBFS(samples []float32) float64 {
 	if len(samples) == 0 {
 		return math.Inf(-1)