improve examples (#708)

examples/client-record-format-opus/dummy_audio.go

@@ -0,0 +1,24 @@
+package main
+
+import "math"
+
+const (
+	sampleRate = 48000
+	frequency  = 400
+	amplitude  = (1 << 14) - 1
+)
+
+func createDummyAudio(pts int64, prevPTS int64) []byte {
+	sampleCount := (pts - prevPTS)
+	n := 0
+	ret := make([]byte, sampleCount*2)
+
+	for i := int64(0); i < sampleCount; i++ {
+		v := int16(amplitude * math.Sin((float64(prevPTS+i)*frequency*math.Pi*2)/sampleRate))
+		ret[n] = byte(v >> 8)
+		ret[n+1] = byte(v)
+		n += 2
+	}
+
+	return ret
+}