Ignore RTP packets with empty payload

### Details

- This PR replaces PR #793 (by @ggarber) with code updated to current v3 and addresses feedback.
- All `XxxxConsumer` classes drop empty RTP packets.
- `RtpStreamRecv` no longer considers empty RTP packets for counter increase and stream activation.
- A substancial change with original PR is that `RtpStreamRecv` accepts those empty packets (otherwise we sould generate NACKs), it's just that those don't account anymore for counter increase and stream activation.

CHANGELOG.md

@@ -3,6 +3,7 @@
 ### NEXT
 
 - `SimulcastConsumer`: Fix increase layer when current layer has not receive SR ([PR #1098](https://github.com/versatica/mediasoup/pull/1098) by @penguinol).
+- Ignore RTP packets with empty payload ([PR #XXXX](https://github.com/versatica/mediasoup/pull/XXXX), credits to @ggarber).
 
 ### 3.14.6
 

worker/include/RTC/RtcLogger.hpp

@@ -21,6 +21,7 @@ namespace RTC
 				INVALID_TARGET_LAYER,
 				UNSUPPORTED_PAYLOAD_TYPE,
 				NOT_A_KEYFRAME,
+				EMPTY_PAYLOAD,
 				SPATIAL_LAYER_MISMATCH,
 				TOO_HIGH_TIMESTAMP_EXTRA_NEEDED,
 				PACKET_PREVIOUS_TO_SPATIAL_LAYER_SWITCH,

worker/src/RTC/PipeConsumer.cpp

@@ -250,6 +250,18 @@ namespace RTC
 		auto& syncRequired  = this->mapRtpStreamSyncRequired.at(rtpStream);
 		auto& rtpSeqManager = this->mapRtpStreamRtpSeqManager.at(rtpStream);
 
+		// Packets with only padding are not forwarded.
+		if (packet->GetPayloadLength() == 0)
+		{
+			rtpSeqManager.Drop(packet->GetSequenceNumber());
+
+#ifdef MS_RTC_LOGGER_RTP
+			packet->logger.Dropped(RtcLogger::RtpPacket::DropReason::EMPTY_PAYLOAD);
+#endif
+
+			return;
+		}
+
 		// If we need to sync, support key frames and this is not a key frame, ignore
 		// the packet.
 		if (syncRequired && this->keyFrameSupported && !packet->IsKeyFrame())

worker/src/RTC/RtcLogger.cpp

@@ -18,6 +18,7 @@ namespace RTC
 			{ RtpPacket::DropReason::INVALID_TARGET_LAYER,                    "InvalidTargetLayer"                 },
 			{ RtpPacket::DropReason::UNSUPPORTED_PAYLOAD_TYPE,                "UnsupportedPayloadType"             },
 			{ RtpPacket::DropReason::NOT_A_KEYFRAME,                          "NotAKeyframe"                       },
+			{ RtpPacket::DropReason::EMPTY_PAYLOAD,                           "EmptyPayload"                       },
 			{ RtpPacket::DropReason::SPATIAL_LAYER_MISMATCH,                  "SpatialLayerMismatch"               },
 			{ RtpPacket::DropReason::TOO_HIGH_TIMESTAMP_EXTRA_NEEDED,         "TooHighTimestampExtraNeeded"        },
 			{ RtpPacket::DropReason::PACKET_PREVIOUS_TO_SPATIAL_LAYER_SWITCH, "PacketPreviousToSpatialLayerSwitch" },

worker/src/RTC/RtpStreamRecv.cpp

@@ -303,6 +303,13 @@ namespace RTC
 		// Calculate Jitter.
 		CalculateJitter(packet->GetTimestamp());
 
+		// Padding only packet, do not consider it for counter increase nor
+		// stream activation.
+		if (packet->GetPayloadLength() == 0)
+		{
+			return true;
+		}
+
 		// Increase transmission counter.
 		this->transmissionCounter.Update(packet);
 
@@ -413,6 +420,13 @@ namespace RTC
 		// NACKed packet.
 		if (this->nackGenerator->ReceivePacket(packet, /*isRecovered*/ true))
 		{
+			// Padding only packet, do not consider it for counter increase nor
+			// stream activation.
+			if (packet->GetPayloadLength() == 0)
+			{
+				return true;
+			}
+
 			// Mark the packet as repaired.
 			RTC::RtpStream::PacketRepaired(packet);
 

worker/src/RTC/SimpleConsumer.cpp

@@ -314,6 +314,18 @@ namespace RTC
 			return;
 		}
 
+		// Packets with only padding are not forwarded.
+		if (packet->GetPayloadLength() == 0)
+		{
+			this->rtpSeqManager.Drop(packet->GetSequenceNumber());
+
+#ifdef MS_RTC_LOGGER_RTP
+			packet->logger.Dropped(RtcLogger::RtpPacket::DropReason::EMPTY_PAYLOAD);
+#endif
+
+			return;
+		}
+
 		auto payloadType = packet->GetPayloadType();
 
 		// NOTE: This may happen if this Consumer supports just some codecs of those

worker/src/RTC/SimulcastConsumer.cpp

@@ -724,6 +724,18 @@ namespace RTC
 			return;
 		}
 
+		// Packets with only padding are not forwarded.
+		if (packet->GetPayloadLength() == 0)
+		{
+			this->rtpSeqManager.Drop(packet->GetSequenceNumber());
+
+#ifdef MS_RTC_LOGGER_RTP
+			packet->logger.Dropped(RtcLogger::RtpPacket::DropReason::EMPTY_PAYLOAD);
+#endif
+
+			return;
+		}
+
 		if (this->targetTemporalLayer == -1)
 		{
 #ifdef MS_RTC_LOGGER_RTP

worker/src/RTC/SvcConsumer.cpp

@@ -639,6 +639,18 @@ namespace RTC
 			return;
 		}
 
+		// Packets with only padding are not forwarded.
+		if (packet->GetPayloadLength() == 0)
+		{
+			this->rtpSeqManager.Drop(packet->GetSequenceNumber());
+
+#ifdef MS_RTC_LOGGER_RTP
+			packet->logger.Dropped(RtcLogger::RtpPacket::DropReason::EMPTY_PAYLOAD);
+#endif
+
+			return;
+		}
+
 		// clang-format off
 		if (
 			this->encodingContext->GetTargetSpatialLayer() == -1 ||