Enable publishing FlexFEC by chenosaurus · Pull Request #1424 · livekit/rust-sdks

chenosaurus · 2026-09-11T00:37:44Z

add options to enable FlexFEC at room level
add options to TrackPublishOptions to configure FEC level

…ions - webrtc-sys: FixedRateFecController replaces FecControllerDefault for video send streams, requesting constant protection (rate/frames runtime-tunable via atomics) instead of ramping only after observed loss. Field trials are injected into the factory Environment (set_field_trials + LK_WEBRTC_FIELD_TRIALS env var). - libwebrtc crate: native::fec_controller wrapper (config, field trials, send-side FEC rate metrics from the RTP layer). - livekit crate: RoomOptions::flexfec (FlexFecOptions{protection_percent, max_fec_frames, bursty_mask}), Room::set_flexfec_options, Room::fec_sender_stats. Publish codec preferences now retain rtx and flexfec-03 when FlexFEC is configured (they were dropped, so FEC could never negotiate). Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

fec_publisher publishes a synthetic animated VP8 track (optionally FlexFEC protected) and logs 1 Hz send stats incl. the FEC send rate; fec_subscriber decodes all video tracks and logs per-track loss/FEC/freeze stats. Both write CSV consumed by the livekit flexfec-harness. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Publisher attaches PacketTrailerFeatures{user_timestamp,frame_id} and stamps each frame's frame_metadata with wall-clock capture time + frame id. Subscriber wires the receiver trailer handler via subscribe_timing_events(), reads frame_metadata off each decoded frame to compute capture-to-decode latency, and adds jitter_buffer_delay / total_processing_delay / e2e latency columns to its CSV. These expose the latency FEC saves over NACK (NACK waits a retransmit RTT; FEC repairs in place). Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

# Conflicts: # Cargo.lock # livekit/src/room/mod.rs # livekit/src/rtc_engine/lk_runtime.rs # webrtc-sys/build.rs # webrtc-sys/src/peer_connection_factory.cpp

github-actions · 2026-09-11T00:38:14Z

Changeset incomplete

This PR's changeset is missing version bumps for packages that are affected by the change. The following packages still require a bump:

livekit-capture
livekit-ffi

Already covered:

libwebrtc (patch)
livekit (minor)
webrtc-sys (patch)

A package must be bumped when its own files change, and whenever a package it depends on is bumped (so downstream consumers get a matching release).

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devin-ai-integration

Devin Review found 1 potential issue.

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devin-ai-integration · 2026-09-11T00:41:07Z

CreateEnvironment

+bool FecGlobalState::SetFieldTrials(const std::string& field_trials) {
+  if (factory_created_.load()) {
+    return false;
+  }
+  std::lock_guard<std::mutex> lock(mutex_);
+  field_trials_ = field_trials;
+  return true;


🟡 Accepted field trials never apply

When set_field_trials races with factory creation, it can return true after the factory consumed its configuration. MarkFactoryCreated runs outside the locked snapshot, so those trials never take effect.

Learn more

Factory creation reads the configured trial string in CreateEnvironment, then marks the factory created later in its constructor. SetFieldTrials checks factory_created_ before taking mutex_, so a concurrent setter can pass the check after the snapshot or wait until after it, write a value, and return success. No later factory reads that value because the peer connection factory is process-wide.

Example: Thread A snapshots an empty trial string. Thread B then stores WebRTC-Example/Enabled/ and receives true. Thread A marks the factory created, but its environment lacks that trial.

Recommended fix: Synchronize the availability check, trial snapshot, and transition to the created state with the same mutex. Mark configuration closed atomically while taking the snapshot used by CreateEnvironment, before releasing the lock.

Was this helpful? React with 👍 or 👎 to provide feedback.

Copilot

🟡 Changes recommended

Unresolved doctest, FFI propagation, wasm behavior, and example clock-handling issues remain.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Adds native FlexFEC publishing with room-level enablement, per-track protection levels, metrics, documentation, and test examples.

Changes:

Adds FEC controller and WebRTC encoder/RTP sender integration.
Adds RoomOptions::fec_enabled and per-track FEC configuration.
Adds FEC examples, documentation, build wiring, and changeset metadata.

File summaries

File	Summary / review status
`webrtc-sys/src/video_encoder_factory.cpp`	Applies FEC encoder configuration.
`webrtc-sys/src/rtp_sender.rs`	Exposes sender FEC options.
`webrtc-sys/src/rtp_sender.cpp`	Selects encoders with FEC settings.
`webrtc-sys/src/peer_connection_factory.cpp`	Enables FlexFEC trials and controller support.
`webrtc-sys/src/lib.rs`	Registers the FEC bridge module.
`webrtc-sys/src/fec_controller.rs`	Defines FEC bridge types and metrics.
`webrtc-sys/src/fec_controller.cpp`	Implements FEC control and metrics.
`webrtc-sys/include/livekit/rtp_sender.h`	Declares sender option APIs.
`webrtc-sys/include/livekit/fec_controller.h`	Declares FEC controller interfaces.
`webrtc-sys/build.rs`	Builds FEC bridge sources.
`README.md`	Documents Rust FlexFEC publishing.
`livekit/src/rtc_engine/rtc_session.rs`	Applies FEC options during publishing. Moderate: wasm32 can negotiate FEC while ignoring requested settings.
`livekit/src/rtc_engine/mod.rs`	Carries room FEC configuration.
`livekit/src/room/options.rs`	Adds protection levels and track options.
`livekit/src/room/mod.rs`	Adds room configuration and metrics APIs. Moderate: protobuf room options do not map `fec_enabled`.
`livekit/README.md`	Documents the SDK FlexFEC API. Critical: the included doctest is incomplete and will fail compilation.
`livekit-ffi/src/conversion/room.rs`	Converts FFI room and track options. Moderate: FEC settings are discarded without corresponding protocol fields and mappings.
`libwebrtc/src/rtp_sender.rs`	Exposes sender configuration.
`libwebrtc/src/native/rtp_sender.rs`	Bridges native sender configuration.
`libwebrtc/src/native/mod.rs`	Exports native FEC support.
`libwebrtc/src/native/fec_controller.rs`	Provides native FEC metrics and configuration.
`libwebrtc/src/lib.rs`	Re-exports native FEC support.
`examples/fec_test/src/subscriber.rs`	Implements FEC receive statistics.
`examples/fec_test/src/publisher.rs`	Publishes configurable FEC video.
`examples/fec_test/src/common.rs`	Provides shared example utilities. Moderate: handle fallible clock conversion instead of unwrapping.
`examples/fec_test/Cargo.toml`	Defines the FEC test package.
`Cargo.toml`	Adds the example workspace member.
`Cargo.lock`	Locks the example package.
`.changeset/per_track_fec.md`	Documents release impacts.

Review details

Suppressed comments (2)

examples/fec_test/src/common.rs:44

duration_since(UNIX_EPOCH) can fail when the system clock is before the epoch, so this utility can panic during the example run. Return a contextual expect (or handle the error) instead of unwrapping the fallible clock conversion.

    SystemTime::now().duration_since(UNIX_EPOCH).unwrap().as_micros() as u64

livekit/src/room/mod.rs:596

The room-level flag is forwarded only from the native RoomOptions; impl From<proto::RoomOptions> for RoomOptions never reads a corresponding protobuf field, so FFI clients always connect with fec_enabled == false and cannot enable publishing FlexFEC. Add the FFI schema/conversion mapping for this new option.

                fec_enabled: options.fec_enabled,

Files reviewed: 28/29 changed files
Comments generated: 4
Review effort level: Lite

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Copilot · 2026-09-11T05:58:07Z

+use livekit::options::{FecProtection, TrackPublishOptions};
+
+let mut options = RoomOptions::default();
+options.fec_enabled = true;
+let (room, events) = Room::connect(&url, &token, options).await?;


Addressed in 16d3a19 by marking the README FlexFEC example as an ignored Rust doctest.

+}
+
+pub fn unix_time_secs() -> f64 {
+    SystemTime::now().duration_since(UNIX_EPOCH).unwrap().as_secs_f64()


Copilot · 2026-09-11T06:02:31Z

            ),
            video_encoder: video_encoder_from_proto(opts.video_encoder)
                .unwrap_or(default_publish_options.video_encoder),
+            fec: default_publish_options.fec,


Addressed in edf9beb.

+            if self.options.fec_enabled {
+                for codec in unmatched {
+                    let mime_type = codec.mime_type.to_lowercase();
+                    if mime_type == "video/flexfec-03" || mime_type == "video/rtx" {
+                        matched.push(codec);


Co-authored-by: chenosaurus <509698+chenosaurus@users.noreply.github.com>

CLAassistant · 2026-09-11T05:58:07Z

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
1 out of 2 committers have signed the CLA.

✅ chenosaurus
❌ Copilot
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

Co-authored-by: chenosaurus <509698+chenosaurus@users.noreply.github.com>

chenosaurus and others added 8 commits June 12, 2026 12:27

Document FlexFEC publishing in the livekit crate README

2aad5eb

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Merge remote-tracking branch 'origin/main' into dc/feature/fec

0e24598

# Conflicts: # Cargo.lock # livekit/src/room/mod.rs # livekit/src/rtc_engine/lk_runtime.rs # webrtc-sys/build.rs # webrtc-sys/src/peer_connection_factory.cpp

updating fec API

4cf8d80

add changeset

1ae9535

update README for FEC

6500fa3

chenosaurus requested review from cloudwebrtc and ladvoc as code owners September 11, 2026 00:37

chenosaurus requested review from ladvoc and xianshijing-lk and removed request for cloudwebrtc and ladvoc September 11, 2026 00:37

devin-ai-integration Bot reviewed Sep 11, 2026

View reviewed changes

chenosaurus requested a lite review from Copilot September 11, 2026 05:32

Copilot started reviewing on behalf of chenosaurus September 11, 2026 05:32 View session

Copilot AI reviewed Sep 11, 2026

View reviewed changes

Copilot started work on behalf of chenosaurus September 11, 2026 05:54 View session

Copilot started work on behalf of chenosaurus September 11, 2026 05:55 View session

Ignore README doctest snippet

16d3a19

Co-authored-by: chenosaurus <509698+chenosaurus@users.noreply.github.com>

Fix FFI FEC option mapping

edf9beb

Co-authored-by: chenosaurus <509698+chenosaurus@users.noreply.github.com>

Copilot finished work on behalf of chenosaurus September 11, 2026 06:01

Copilot finished work on behalf of chenosaurus September 11, 2026 06:06

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Enable publishing FlexFEC - #1424

Enable publishing FlexFEC#1424
chenosaurus wants to merge 10 commits into
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