From 34b934693fbcd164dec0f2297ec358a2095b9c58 Mon Sep 17 00:00:00 2001
From: Anunay Maheshwari <anunay@livekit.io>
Date: Sat, 31 May 2025 22:08:34 +0530
Subject: [PATCH 1/4] fix(sampleWriter): handle dropped packets

---
 pcm.go | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/pcm.go b/pcm.go
index 1e22246..da78518 100644
--- a/pcm.go
+++ b/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.

From 12b1dee09819cabff75b66e00c1929f22abab666 Mon Sep 17 00:00:00 2001
From: Anunay Maheshwari <anunay@livekit.io>
Date: Sun, 1 Jun 2025 00:36:58 +0530
Subject: [PATCH 2/4] feat(opus): support dtx encoding

---
 opus/opus.go | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/opus/opus.go b/opus/opus.go
index 4b2af7c..d1e1109 100644
--- a/opus/opus.go
+++ b/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])
 }
 

From 607419611b200ca3a24c3d76b4edaea676f1a2ae Mon Sep 17 00:00:00 2001
From: Anunay Maheshwari <anunay@livekit.io>
Date: Sun, 1 Jun 2025 11:10:21 +0530
Subject: [PATCH 3/4] fix: add tolerance to PrevPacketsDropped calculation

---
 pcm.go | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/pcm.go b/pcm.go
index da78518..9254d80 100644
--- a/pcm.go
+++ b/pcm.go
@@ -204,7 +204,8 @@ func (w *sampleWriter[T]) WriteSample(in T) error {
 	var droppedPackets uint16
 	if !w.lastWrite.IsZero() {
 		timeSinceLastWrite := time.Since(w.lastWrite)
-		if timeSinceLastWrite > w.sampleDur {
+		tolerance := w.sampleDur / 10
+		if timeSinceLastWrite > w.sampleDur+tolerance {
 			droppedPackets = uint16((timeSinceLastWrite - w.sampleDur) / w.sampleDur)
 		}
 	}

From 1a044d5f6d13784f25f9feb4cd7ed466c08f63d3 Mon Sep 17 00:00:00 2001
From: Anunay Maheshwari <anunay@livekit.io>
Date: Sun, 1 Jun 2025 20:31:17 +0530
Subject: [PATCH 4/4] fix(PrevDroppedPackets): use tolerance in calculation

---
 pcm.go | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/pcm.go b/pcm.go
index 9254d80..52b2ea9 100644
--- a/pcm.go
+++ b/pcm.go
@@ -205,8 +205,8 @@ func (w *sampleWriter[T]) WriteSample(in T) error {
 	if !w.lastWrite.IsZero() {
 		timeSinceLastWrite := time.Since(w.lastWrite)
 		tolerance := w.sampleDur / 10
-		if timeSinceLastWrite > w.sampleDur+tolerance {
-			droppedPackets = uint16((timeSinceLastWrite - w.sampleDur) / w.sampleDur)
+		if timeSinceLastWrite > (w.sampleDur + tolerance) {
+			droppedPackets = uint16((timeSinceLastWrite - (w.sampleDur - tolerance)) / w.sampleDur)
 		}
 	}