Simulcast frozen video due to dropping RTP packets

[quanli168]

Bug Report

We recently upgraded mediasoup from version 3.12.13 to 3.14.7 and noticed that video freezing has become more frequent since the upgrade. After enabling additional mediasoup logging, we believe this issue is due to a regression introduced in this pull request.

The problem occurs under the following conditions:

1. The producer has two simulcast streams (SSRC-A and SSRC-B).
2. The simulcast consumer is consuming SSRC-B.
3. SSRC-A has a packet that contains only padding. Let's assume this packet's sequence number is SEQ-1. This packet is dropped and stored in the rtpSeqManager https://github.com/versatica/mediasoup/blob/06f66e62874ede5f4bb4a166ba2629280b9edada/worker/src/RTC/SimpleConsumer.cpp#L320
4. SSRC-B then sends an RTP packet with the same sequence number. Since this sequence number is in rtpSeqManager's dropped list, it is assigned a sequence number of 0. https://github.com/versatica/mediasoup/blob/06f66e62874ede5f4bb4a166ba2629280b9edada/worker/src/RTC/SimpleConsumer.cpp#L394
5. The packet is then dropped because its sequence number is 0 https://github.com/versatica/mediasoup/blob/06f66e62874ede5f4bb4a166ba2629280b9edada/worker/src/RTC/SimpleConsumer.cpp#L432

Attached are logs showing that RTP packets with sequence numbers 42015-42134 were dropped due to this scenario. exportedLogRecords.CSV

Your environment

• Operating system:
• Node version:
• npm version:
• gcc/clang version:
• mediasoup version: 3.14.7
• mediasoup-client version:

Issue description

[ibc]

Thanks for the report. Will look soon.

[ibc]

The problem is that SimulcastConsumer::SendRtpPacket() method is dropping the packet and calling this->rtpSeqManager.Drop even if the packet doesn't below to the simulcast stream being sent to the consumer.

[ibc]

CC @ggarber

[ibc]

PR done here: https://github.com/versatica/mediasoup/pull/1431

Once merged, will release. Thanks a lot!