From 87e90369762c19c19338ac201769bee5ebc672d3 Mon Sep 17 00:00:00 2001
From: aler9 <46489434+aler9@users.noreply.github.com>
Date: Wed, 26 Oct 2022 16:53:27 +0200
Subject: [PATCH] rtptimedec: increase threshold of negative differences

---
 pkg/rtptimedec/decoder.go      | 26 +++++++++++++-------------
 pkg/rtptimedec/decoder_test.go | 14 +++++++-------
 2 files changed, 20 insertions(+), 20 deletions(-)

diff --git a/pkg/rtptimedec/decoder.go b/pkg/rtptimedec/decoder.go
index 97d2bc16..ed3ceb4b 100644
--- a/pkg/rtptimedec/decoder.go
+++ b/pkg/rtptimedec/decoder.go
@@ -5,14 +5,14 @@ import (
 	"time"
 )
 
-const negativeThreshold = 0xFFFFFFF
+const negativeThreshold = 0xFFFFFFFF / 2
 
 // Decoder is a RTP timestamp decoder.
 type Decoder struct {
 	clockRate   time.Duration
 	initialized bool
-	tsOverall   time.Duration
-	tsPrev      uint32
+	overall     time.Duration
+	prev        uint32
 }
 
 // New allocates a Decoder.
@@ -26,25 +26,25 @@ func New(clockRate int) *Decoder {
 func (d *Decoder) Decode(ts uint32) time.Duration {
 	if !d.initialized {
 		d.initialized = true
-		d.tsPrev = ts
+		d.prev = ts
 		return 0
 	}
 
-	diff := ts - d.tsPrev
+	diff := ts - d.prev
 
 	// negative difference
 	if diff > negativeThreshold {
-		diff = d.tsPrev - ts
-		d.tsPrev = ts
-		d.tsOverall -= time.Duration(diff)
+		diff = d.prev - ts
+		d.prev = ts
+		d.overall -= time.Duration(diff)
 	} else {
-		d.tsPrev = ts
-		d.tsOverall += time.Duration(diff)
+		d.prev = ts
+		d.overall += time.Duration(diff)
 	}
 
-	// avoid an int64 overflow and preserve resolution by splitting division into two parts:
+	// avoid an int64 overflow and keep resolution by splitting division into two parts:
 	// first add the integer part, then the decimal part.
-	secs := d.tsOverall / d.clockRate
-	dec := d.tsOverall % d.clockRate
+	secs := d.overall / d.clockRate
+	dec := d.overall % d.clockRate
 	return secs*time.Second + dec*time.Second/d.clockRate
 }
diff --git a/pkg/rtptimedec/decoder_test.go b/pkg/rtptimedec/decoder_test.go
index 5286a070..cb33ab56 100644
--- a/pkg/rtptimedec/decoder_test.go
+++ b/pkg/rtptimedec/decoder_test.go
@@ -30,13 +30,13 @@ func TestNegativeDiff(t *testing.T) {
 func TestOverflow(t *testing.T) {
 	d := New(90000)
 
-	i := uint32(4294877296)
+	i := uint32(0xFFFFFFFF - 90000 + 1)
 	secs := time.Duration(0)
 	pts := d.Decode(i)
 	require.Equal(t, time.Duration(0), pts)
 
-	const stride = 150
-	lim := uint32(uint64(4294967296 - (stride * 90000)))
+	const stride = 1500
+	lim := uint32(uint64(0xFFFFFFFF + 1 - (stride * 90000)))
 
 	for n := 0; n < 100; n++ {
 		// overflow
@@ -59,19 +59,19 @@ func TestOverflow(t *testing.T) {
 func TestOverflowAndBack(t *testing.T) {
 	d := New(90000)
 
-	pts := d.Decode(4294877296)
+	pts := d.Decode(0xFFFFFFFF - 90000 + 1)
 	require.Equal(t, time.Duration(0), pts)
 
 	pts = d.Decode(90000)
 	require.Equal(t, 2*time.Second, pts)
 
-	pts = d.Decode(4294877296)
+	pts = d.Decode(0xFFFFFFFF - 90000 + 1)
 	require.Equal(t, time.Duration(0), pts)
 
-	pts = d.Decode(4294877296 - 90000)
+	pts = d.Decode(0xFFFFFFFF - 90000 + 1 - 90000)
 	require.Equal(t, -1*time.Second, pts)
 
-	pts = d.Decode(4294877296)
+	pts = d.Decode(0xFFFFFFFF - 90000 + 1)
 	require.Equal(t, time.Duration(0), pts)
 
 	pts = d.Decode(90000)