fix(sampleWriter): handle dropped packets & opus dtx

opus/opus.go

@@ -64,7 +64,7 @@ func Decode(w media.PCM16Writer, targetChannels int, logger logger.Logger) (Writ
 	}, nil
 }
 
-func Encode(w Writer, channels int, logger logger.Logger) (media.PCM16Writer, error) {
+func Encode(w Writer, channels int, useDtx bool, logger logger.Logger) (media.PCM16Writer, error) {
 	enc, err := opus.NewEncoder(w.SampleRate(), channels, opus.AppVoIP)
 	if err != nil {
 		return nil, err
@@ -73,6 +73,7 @@ func Encode(w Writer, channels int, logger logger.Logger) (media.PCM16Writer, er
 		w:      w,
 		enc:    enc,
 		buf:    make([]byte, w.SampleRate()/rtp.DefFramesPerSec*channels),
+		useDtx: useDtx,
 		logger: logger,
 	}, nil
 }
@@ -162,6 +163,7 @@ type encoder struct {
 	w      Writer
 	enc    *opus.Encoder
 	buf    Sample
+	useDtx bool
 	logger logger.Logger
 }
 
@@ -178,6 +180,13 @@ func (e *encoder) WriteSample(in media.PCM16Sample) error {
 	if err != nil {
 		return err
 	}
+
+	// opus_encode() returns the number of bytes actually written to the packet.
+	// The return value can be negative, which indicates that an error has occurred.
+	// If the return value is 1 byte, then the packet does not need to be transmitted (DTX).
+	if n == 1 && e.useDtx {
+		return nil
+	}
 	return e.w.WriteSample(e.buf[:n])
 }
 

pcm.go

@@ -182,6 +182,7 @@ type sampleWriter[T ~[]byte] struct {
 	w          MediaSampleWriter
 	sampleRate int
 	sampleDur  time.Duration
+	lastWrite  time.Time
 }
 
 func (w *sampleWriter[T]) String() string {
@@ -199,7 +200,17 @@ func (w *sampleWriter[T]) Close() error {
 func (w *sampleWriter[T]) WriteSample(in T) error {
 	data := make([]byte, len(in))
 	copy(data, in)
-	return w.w.WriteSample(media.Sample{Data: data, Duration: w.sampleDur})
+
+	var droppedPackets uint16
+	if !w.lastWrite.IsZero() {
+		timeSinceLastWrite := time.Since(w.lastWrite)
+		if timeSinceLastWrite > w.sampleDur {
+			droppedPackets = uint16((timeSinceLastWrite - w.sampleDur) / w.sampleDur)
+		}
+	}
+
+	w.lastWrite = time.Now()
+	return w.w.WriteSample(media.Sample{Data: data, Duration: w.sampleDur, PrevDroppedPackets: droppedPackets})
 }
 
 // MonoToStereo converts mono PCM from src to stereo PCM in dst.