SampleBuilder: keep track of padding packets

We store the last timestamp as a nil value at first to distinguish between no timestamp received and subsequent timestamps.
pion · Jan 4, 2023 · 46b9041 · 46b9041
1 parent 336fb31
commit 46b9041
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Showing 3 changed files with 37 additions and 13 deletions.
diff --git a/pkg/media/media.go b/pkg/media/media.go
@@ -14,6 +14,7 @@ type Sample struct {
 	Duration           time.Duration
 	PacketTimestamp    uint32
 	PrevDroppedPackets uint16
+	PrevPaddingPackets uint16
 }
 
 // Writer defines an interface to handle

diff --git a/pkg/media/samplebuilder/samplebuilder.go b/pkg/media/samplebuilder/samplebuilder.go
@@ -35,8 +35,13 @@ type SampleBuilder struct {
 	// prepared contains the samples that have been processed to date
 	prepared sampleSequenceLocation
 
+	lastSampleTimestamp *uint32
+
 	// number of packets forced to be dropped
 	droppedPackets uint16
+
+	// number of padding packets detected and dropped (this will be a subset of `droppedPackets`)
+	paddingPackets uint16
 }
 
 // New constructs a new SampleBuilder.
@@ -185,6 +190,7 @@ const secondToNanoseconds = 1000000000
 // buildSample creates a sample from a valid collection of RTP Packets by
 // walking forwards building a sample if everything looks good clear and
 // update buffer+values
+// nolint: gocognit
 func (s *SampleBuilder) buildSample(purgingBuffers bool) *media.Sample {
 	if s.active.empty() {
 		s.active = s.filled
@@ -242,7 +248,17 @@ func (s *SampleBuilder) buildSample(purgingBuffers bool) *media.Sample {
 	// prior to decoding all the packets, check if this packet
 	// would end being disposed anyway
 	if !s.depacketizer.IsPartitionHead(s.buffer[consume.head].Payload) {
+		// libwebrtc may send empty padding packets to smooth out send rate. These packets do not carry any media payloads.
+		isPadding := false
+		for i := consume.head; i != consume.tail; i++ {
+			if s.lastSampleTimestamp != nil && *s.lastSampleTimestamp == s.buffer[i].Timestamp && len(s.buffer[i].Payload) == 0 {
+				isPadding = true
+			}
+		}
 		s.droppedPackets += consume.count()
+		if isPadding {
+			s.paddingPackets += consume.count()
+		}
 		s.purgeConsumedLocation(consume, true)
 		s.purgeConsumedBuffers()
 		return nil
@@ -264,9 +280,13 @@ func (s *SampleBuilder) buildSample(purgingBuffers bool) *media.Sample {
 		Duration:           time.Duration((float64(samples)/float64(s.sampleRate))*secondToNanoseconds) * time.Nanosecond,
 		PacketTimestamp:    sampleTimestamp,
 		PrevDroppedPackets: s.droppedPackets,
+		PrevPaddingPackets: s.paddingPackets,
 	}
 
 	s.droppedPackets = 0
+	s.paddingPackets = 0
+	s.lastSampleTimestamp = new(uint32)
+	*s.lastSampleTimestamp = sampleTimestamp
 
 	s.preparedSamples[s.prepared.tail] = sample
 	s.prepared.tail++

diff --git a/pkg/media/samplebuilder/samplebuilder_test.go b/pkg/media/samplebuilder/samplebuilder_test.go
@@ -37,6 +37,7 @@ func (f *fakeDepacketizer) IsPartitionHead(payload []byte) bool {
 		return true
 	}
 
+	// skip padding
 	if len(payload) < 1 {
 		return false
 	}
@@ -233,21 +234,23 @@ func TestSampleBuilder(t *testing.T) {
 			// shamelessly stolen from webrtc-rs
 			message: "Sample builder should recognize padding packets",
 			packets: []*rtp.Packet{
-				{Header: rtp.Header{SequenceNumber: 5000, Timestamp: 1}, Payload: []byte{1}},
-				{Header: rtp.Header{SequenceNumber: 5001, Timestamp: 1}, Payload: []byte{2}},
-				{Header: rtp.Header{SequenceNumber: 5002, Timestamp: 1, Marker: true}, Payload: []byte{3}},
-				{Header: rtp.Header{SequenceNumber: 5003, Timestamp: 1}, Payload: []byte{}},
-				{Header: rtp.Header{SequenceNumber: 5004, Timestamp: 1}, Payload: []byte{}},
-				{Header: rtp.Header{SequenceNumber: 5005, Timestamp: 3}, Payload: []byte{1}},
-				{Header: rtp.Header{SequenceNumber: 5006, Timestamp: 3, Marker: true}, Payload: []byte{7}},
-				{Header: rtp.Header{SequenceNumber: 5007, Timestamp: 4}, Payload: []byte{1}},
+				{Header: rtp.Header{SequenceNumber: 5000, Timestamp: 1}, Payload: []byte{1}},               // 1st packet
+				{Header: rtp.Header{SequenceNumber: 5001, Timestamp: 1}, Payload: []byte{2}},               // 2nd packet
+				{Header: rtp.Header{SequenceNumber: 5002, Timestamp: 1, Marker: true}, Payload: []byte{3}}, // 3rd packet
+				{Header: rtp.Header{SequenceNumber: 5003, Timestamp: 1}, Payload: []byte{}},                // Padding packet 1
+				{Header: rtp.Header{SequenceNumber: 5004, Timestamp: 1}, Payload: []byte{}},                // Padding packet 2
+				{Header: rtp.Header{SequenceNumber: 5005, Timestamp: 3}, Payload: []byte{1}},               // 6th packet
+				{Header: rtp.Header{SequenceNumber: 5006, Timestamp: 3, Marker: true}, Payload: []byte{7}}, // 7th packet
+				{Header: rtp.Header{SequenceNumber: 5007, Timestamp: 4}, Payload: []byte{1}},               // 7th packet
 			},
 			withHeadChecker: true,
 			headBytes:       []byte{1},
 			samples: []*media.Sample{
-				{Data: []byte{1, 2, 3}, Duration: 0, PacketTimestamp: 1},
+				{Data: []byte{1, 2, 3}, Duration: 0, PacketTimestamp: 1, PrevDroppedPackets: 0}, // first sample
 			},
-			maxLate: 50,
+			maxLate:          50,
+			maxLateTimestamp: 2000,
+			extraPopAttempts: 1,
 		},
 		{
 			// shamelessly stolen from webrtc-rs
@@ -260,10 +263,10 @@ func TestSampleBuilder(t *testing.T) {
 				{Header: rtp.Header{SequenceNumber: 5004, Timestamp: 2, Marker: true}, Payload: []byte{1}}, // 3rd valid packet
 				{Header: rtp.Header{SequenceNumber: 5005, Timestamp: 3}, Payload: []byte{1}},               // 4th valid packet, start of next sample
 			},
-			withHeadChecker:  true,
-			headBytes: []byte{1},
+			withHeadChecker: true,
+			headBytes:       []byte{1},
 			samples: []*media.Sample{
-				{Data: []byte{1, 2}, Duration: 0, PacketTimestamp: 1, PrevDroppedPackets: 0},                                                             // 1st sample
+				{Data: []byte{1, 2}, Duration: 0, PacketTimestamp: 1, PrevDroppedPackets: 0}, // 1st sample
 			},
 			maxLate:          50,
 			maxLateTimestamp: 2000,