fix(packet_pool): align discontinuity detection with FFmpeg behavior (#70)

* Added devcontainer

* fix(packet_pool): align discontinuity detection with FFmpeg behavior

- Added check for PIDNull to skip discontinuity detection (matches FFmpeg's handling)
- Fixed adaptation field discontinuity indicator logic (matches FFmpeg's specification)
- Improved continuity counter validation to match FFmpeg's implementation
- Updated test case to reflect FFmpeg-compliant behavior

BREAKING CHANGE: The function now follows FFmpeg's rules for PIDNull and
adaptation field discontinuity indicators, which were previously handled differently.

Test case in packet_pool_test.go has been updated to match FFmpeg's expected behavior.

* chore(packet_pool_test): add test cases for PIDNull and empty packet list

Adds two new test cases to the hasDiscontinuity function:
- Verifies that a packet with PIDNull does not trigger a discontinuity
- Tests handling of empty packet lists when checking against a packet with continuity counter

* fix: correct trailing newline in Dockerfile and remove tmp/.gitignore due to rebase

---------

Co-authored-by: Quentin Renard <contact-github@asticode.com>

Author: secit

packet_pool.go

@@ -118,9 +118,31 @@ func (b *packetPool) dumpUnlocked() (ps []*Packet) {
 
 // hasDiscontinuity checks whether a packet is discontinuous with a set of packets
 func hasDiscontinuity(ps []*Packet, p *Packet) bool {
+	if p.Header.PID == PIDNull {
+		return false
+	}
+
+	isDiscontinuityIndicator := p.Header.HasAdaptationField && p.AdaptationField.DiscontinuityIndicator
+	if isDiscontinuityIndicator {
+		return false
+	}
+
 	l := len(ps)
-	return (p.Header.HasAdaptationField && p.AdaptationField.DiscontinuityIndicator) || (l > 0 && ((p.Header.HasPayload && p.Header.ContinuityCounter != (ps[l-1].Header.ContinuityCounter+1)%16) ||
-		(!p.Header.HasPayload && p.Header.ContinuityCounter != ps[l-1].Header.ContinuityCounter)))
+	if l == 0 {
+		return false
+	}
+
+	var expectedContinuityCounter uint8
+	if p.Header.HasPayload {
+		expectedContinuityCounter = (ps[l-1].Header.ContinuityCounter + 1) & 0x0f
+	} else {
+		expectedContinuityCounter = ps[l-1].Header.ContinuityCounter
+	}
+	if expectedContinuityCounter == p.Header.ContinuityCounter {
+		return false
+	}
+
+	return true
 }
 
 // isSameAsPrevious checks whether a packet is the same as the last packet of a set of packets

packet_pool_test.go

@@ -9,7 +9,9 @@ import (
 func TestHasDiscontinuity(t *testing.T) {
 	assert.False(t, hasDiscontinuity([]*Packet{{Header: PacketHeader{ContinuityCounter: 15}}}, &Packet{Header: PacketHeader{ContinuityCounter: 0, HasPayload: true}}))
 	assert.False(t, hasDiscontinuity([]*Packet{{Header: PacketHeader{ContinuityCounter: 15}}}, &Packet{Header: PacketHeader{ContinuityCounter: 15}}))
-	assert.True(t, hasDiscontinuity([]*Packet{{Header: PacketHeader{ContinuityCounter: 15}}}, &Packet{AdaptationField: &PacketAdaptationField{DiscontinuityIndicator: true}, Header: PacketHeader{ContinuityCounter: 0, HasAdaptationField: true, HasPayload: true}}))
+	assert.False(t, hasDiscontinuity([]*Packet{{Header: PacketHeader{ContinuityCounter: 15}}}, &Packet{AdaptationField: &PacketAdaptationField{DiscontinuityIndicator: true}, Header: PacketHeader{ContinuityCounter: 0, HasAdaptationField: true, HasPayload: true}}))
+	assert.False(t, hasDiscontinuity([]*Packet{{Header: PacketHeader{ContinuityCounter: 15}}}, &Packet{Header: PacketHeader{PID: PIDNull}}))
+	assert.False(t, hasDiscontinuity([]*Packet{}, &Packet{Header: PacketHeader{ContinuityCounter: 5}}))
 	assert.True(t, hasDiscontinuity([]*Packet{{Header: PacketHeader{ContinuityCounter: 15}}}, &Packet{Header: PacketHeader{ContinuityCounter: 1, HasPayload: true}}))
 	assert.True(t, hasDiscontinuity([]*Packet{{Header: PacketHeader{ContinuityCounter: 15}}}, &Packet{Header: PacketHeader{ContinuityCounter: 0}}))
 }