Better compliance with the DTMF RFC4733 (#126)

Better compliance with the DTMF RFC4733.

Author: dennwc

pkg/media/dtmf/dtmf.go

@@ -264,20 +264,34 @@ func Write(ctx context.Context, audio media.PCM16Writer, events *rtp.Stream, dig
 		// generate telephony events
 		if events != nil && len(freq) != 0 {
 			dur := step + totalDur - remaining
+			first := totalDur == remaining
+			end := remaining-step <= 0
 
 			n, err := Encode(buf[:], Event{
 				Code:   code,
 				Volume: eventVolume,
 				Dur:    uint16(dur / (time.Second / SampleRate)),
-				End:    remaining-step <= 0,
+				End:    end,
 			})
 			if err != nil {
 				return err
 			}
-			err = events.WritePayload(buf[:n], totalDur == remaining)
+			// all packets for a digit must be sent with the same timestamp
+			err = events.WritePayloadAtCurrent(buf[:n], first)
 			if err != nil {
 				return err
 			}
+			if end {
+				// must repeat edn event 3 times, as per RFC
+				if err = events.WritePayloadAtCurrent(buf[:n], first); err != nil {
+					return err
+				}
+				if err = events.WritePayloadAtCurrent(buf[:n], first); err != nil {
+					return err
+				}
+				// advance the timestamp now
+				events.Delay(uint32(totalDur / (time.Second / SampleRate)))
+			}
 		}
 		remaining -= step
 		ts += step

pkg/media/dtmf/dtmf_test.go

@@ -78,16 +78,74 @@ func TestDTMFDelay(t *testing.T) {
 	w := rtp.NewSeqWriter(&buf).NewStream(101, SampleRate)
 	err := Write(context.Background(), nil, w, "1w23")
 	require.NoError(t, err)
-	require.Len(t, buf, 39)
+
 	const packetDur = uint32(SampleRate / int(time.Second/rtp.DefFrameDur))
-	for i, p := range buf {
-		ts := packetDur * uint32(i)
-		if i >= 26 {
-			ts += 4 * (SampleRate / 4) // 2 * 250ms + 500ms
-		} else if i >= 13 {
-			ts += 3 * (SampleRate / 4) // 250ms after tone + 500ms user-defined
+	type packet struct {
+		SequenceNumber uint16
+		Timestamp      uint32
+		Marker         bool
+		Event
+	}
+	var (
+		exp []packet
+		seq uint16
+		ts  uint32
+	)
+	expectDigit := func(code byte, digit byte) {
+		start := ts
+		const n = 13
+		for i := 0; i < n-1; i++ {
+			exp = append(exp, packet{
+				SequenceNumber: seq,
+				Timestamp:      start, // should be the same for all events
+				Marker:         i == 0,
+				Event: Event{
+					Code:   code,
+					Digit:  digit,
+					Volume: eventVolume,
+					Dur:    uint16(i+1) * uint16(packetDur),
+					End:    false,
+				},
+			})
+			ts += packetDur
+			seq++
+		}
+		// end event must be sent 3 times with the same duration
+		for i := 0; i < 3; i++ {
+			exp = append(exp, packet{
+				SequenceNumber: seq,
+				Timestamp:      start, // should be the same for all events
+				Marker:         false,
+				Event: Event{
+					Code:   code,
+					Digit:  digit,
+					Volume: eventVolume,
+					Dur:    uint16(n) * uint16(packetDur),
+					End:    true,
+				},
+			})
+			seq++
 		}
-		require.EqualValues(t, uint16(i), p.SequenceNumber)
-		require.EqualValues(t, ts, p.Timestamp, "i=%d, dt=%v", i, p.Timestamp-ts)
+		ts += packetDur
+		// delay between digits
+		ts += uint32(eventDur / (time.Second / SampleRate))
+		// rounding error (12.5 events in a sec)
+		ts -= packetDur / 2
+	}
+	expectDigit(1, '1')
+	ts += SampleRate / 2 // 500ms delay
+	expectDigit(2, '2')
+	expectDigit(3, '3')
+	var got []packet
+	for _, p := range buf {
+		e, err := Decode(p.Payload)
+		require.NoError(t, err)
+		got = append(got, packet{
+			SequenceNumber: p.SequenceNumber,
+			Timestamp:      p.Timestamp,
+			Marker:         p.Marker,
+			Event:          e,
+		})
 	}
+	require.Equal(t, exp, got)
 }

pkg/media/rtp/rtp.go

@@ -124,18 +124,30 @@ type Stream struct {
 	ev        Event
 }
 
-func (s *Stream) WritePayload(data []byte, marker bool) error {
+func (s *Stream) writePayload(inc bool, data []byte, marker bool) error {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 	s.ev.Payload = data
 	s.ev.Marker = marker
 	if err := s.s.WriteEvent(&s.ev); err != nil {
 		return err
 	}
-	s.ev.Timestamp += s.packetDur
+	if inc {
+		s.ev.Timestamp += s.packetDur
+	}
 	return nil
 }
 
+// WritePayload writes the payload to RTP and increments the timestamp.
+func (s *Stream) WritePayload(data []byte, marker bool) error {
+	return s.writePayload(true, data, marker)
+}
+
+// WritePayloadAtCurrent writes the payload to RTP at the current timestamp.
+func (s *Stream) WritePayloadAtCurrent(data []byte, marker bool) error {
+	return s.writePayload(false, data, marker)
+}
+
 func (s *Stream) Delay(dur uint32) {
 	s.mu.Lock()
 	defer s.mu.Unlock()