Implements FlexFEC-03 (RFC 8627) end to end in the SFU, in both directions:
- Upstream: decode FlexFEC repair packets from publishers and recover lost
media in the receive buffer before forwarding (pkg/sfu/flexfec/decoder.go,
pkg/sfu/buffer). Recovered packets are surfaced via Prometheus counters.
- Downstream: generate FlexFEC for subscribers off the downtrack, paced
alongside media (pkg/sfu/downtrack_fec.go, pkg/sfu/pacer).
- Negotiation: advertise and match flexfec-03 in the media engine and
transport SDP, gated by new config knobs (pkg/rtc, pkg/config,
config-sample.yaml).
- Telemetry: livekit_fec_* metrics for sent/received/recovered packets
(pkg/telemetry/prometheus/packets.go).
Tests: unit coverage for the decoder, buffer recovery, downtrack generation,
and transport negotiation, plus an end-to-end integration test and the
test-client support it needs (test/flexfec_test.go, test/client).
* Buffer size config for video and audio.
There was only one buffer size in config.
In upstream, config value was used for video.
Audio used a hard coded value of 200 packets.
But, in the down stream sequencer, the config value was used for both
video and audio. So, if video was set up for high bit rate (deep
buffers), audio sequencer ended up using a lot of memory too in
sequencer.
Split config to be able to control that and also not hard code audio.
Another optimisation here would be to not instantiate sequencer unkess
NACK is negotiated.
* deprecate packet_buffer_size
* Separate from ion-sfu
changes:
1. extract pkg/buffer, twcc, sfu, relay, stats, logger
2. to solve cycle import, move ion-sfu/pkg/logger to pkg/sfu/logger
3. replace pion/ion-sfu => ./
reason: will change import pion/ion-sfu/pkg/* to livekit-server/pkg/*
after this pr merged. Just not change any code in this pr, because it
will confused with the separate code from ion-sfu in review.
* Move code from ion-sfu to pkg/sfu
* fix build error for resovle conflict
Co-authored-by: cnderrauber <zengjie9004@gmail.com>
David Chen