rustrtc

A high-performance, full-stack real-time communication library — WebRTC, RTP/SRTP, T.38 Fax, and UPnP NAT traversal — all through a unified PeerConnection API.

Features

• High performance — ~3.4× faster than webrtc-rs and ~3.2× faster than pion (Go) in throughput, with ~47% less memory than webrtc-rs (see the benchmark below).
• Full protocol stack — WebRTC, RTP, SRTP, and T.38 fax in a single library, plus UPnP IGD NAT traversal. Few moving parts, no missing pieces.
• Unified PeerConnection API — one interface for every transport mode (WebRtc ICE/DTLS/SRTP, Srtp, Rtp, and T.38). No fragmented APIs.
• WebRTC compliant — interoperable with Chrome/WebRTC and pion; offer/answer, renegotiation, rollback, and standard SDP attributes.
• ICE restart — restart_ice() for network migration / re-INVITE flows, with automatic detection of remote-initiated restarts (RFC 8445 §9).
• Complete media pipeline — packetizer/depacketizer (VP8, VP9, H264, Opus, G.711/G.722/G.729), jitter buffer, NACK/RTX, FIR/PLI, TWCC, and REMB for audio and video.
• Bandwidth estimation (GCC) — generates TWCC receiver feedback, stamps transport-wide sequence numbers on outbound RTP, and exposes a live target_bitrate estimate for encoder adaptation (RtpSender::subscribe_target_bitrate).
• Full ICE — STUN, TURN (UDP + TCP), ICE Lite, ICE TCP (RFC 6544), single-port UDP mux for SFU/WHEP deployments, and mDNS candidate obfuscation (enable_mdns).
• NAT traversal & deployment — RTP latching, UPnP IGD port mapping, and firewall-friendly port ranges (rtp_start_port/rtp_end_port).
• Production extras — RTP rewrite bridge (SSRC/PT/sequence remapping) and a WebRTC-compatible stats model.

Benchmark (rustrtc vs webrtc-rs & pion)

Fresh 3-way comparison (cargo run -r --example benchmark builds the webrtc-rs and pion harnesses automatically):

Key findings:

• Throughput: rustrtc is ~3.4× faster than webrtc-rs and ~3.2× faster than pion, with no regression after adding ICE restart, mDNS, VP9, and the TWCC/GCC pipeline.
• Memory: rustrtc uses ~47% less memory than webrtc-rs and ~61% less than pion.
• Setup latency: 0.57 ms vs 3.09 ms (webrtc-rs) / 1.20 ms (pion).

Reproduce with cargo run -r --example benchmark (numbers above from an 8-core x86-64 Linux box, rustc 1.97 / go1.24; absolute values scale with hardware — the ratios are the stable signal).

Usage

Here is a simple example of how to create a PeerConnection and handle an offer:

use rustrtc::{PeerConnection, RtcConfiguration, SessionDescription, SdpType};

#[tokio::main]
async fn main() {
    let config = RtcConfiguration::default();
    let pc = PeerConnection::new(config);

    // Create a Data Channel
    let dc = pc.create_data_channel("data", None).unwrap();

    // Handle received messages
    let dc_clone = dc.clone();
    tokio::spawn(async move {
        while let Some(event) = dc_clone.recv().await {
            if let rustrtc::DataChannelEvent::Message(data) = event {
                println!("Received: {:?}", String::from_utf8_lossy(&data));
            }
        }
    });

    // Create an offer
    let offer = pc.create_offer().unwrap();
    pc.set_local_description(offer).unwrap();

    // Wait for ICE gathering to complete
    pc.wait_for_gathering_complete().await;

    // Get the complete SDP with candidates
    let complete_offer = pc.local_description().unwrap();
    println!("Offer SDP: {}", complete_offer.to_sdp_string());
}

Configuration

All configuration goes through RtcConfiguration (or its builder RtcConfigurationBuilder):

Transport & Network

• transport_mode — TransportMode::WebRtc (default), TransportMode::Srtp, or TransportMode::Rtp.
• ice_servers — STUN/TURN server list.
• ice_transport_policy — All or Relay.
• rtp_start_port / rtp_end_port — Restrict RTP/ICE to a port range.
• external_ip — Override the external IP for ICE candidates (NAT scenarios).
• bind_ip — Bind to a specific local IP.
• disable_ipv6 — Disable IPv6 candidate gathering.
• enable_ice_lite — Enable ICE Lite mode.
• ice_tcp_policy — IceTcpPolicy::Disabled (default), IceTcpPolicy::Enabled, or IceTcpPolicy::PassiveOnly. Controls ICE TCP candidate support per RFC 6544.
• ice_udp_mux / ice_udp_mux_port — Share a single UDP socket across many PeerConnections (single-port multiplexing for SFU/WHEP). Set ice_udp_mux = true and ice_udp_mux_port = <port>; incoming packets are demuxed by the server ufrag in the STUN Binding Request, then by remote source address.
• enable_mdns — Advertise host candidates via mDNS (<random>.local hostnames instead of local IPs, draft-ietf-rtcweb-mdns). A built-in mDNS responder answers A/AAAA lookups; real addresses are kept internally so connectivity is unaffected. Default: false.

Bandwidth Estimation (GCC)

• enable_gcc — TWCC + GCC loop (default: true): outbound RTP is stamped with transport-cc sequence numbers, TWCC feedback is generated for inbound streams, and each RtpSender publishes a bandwidth estimate. The library does not throttle sends itself — drive your encoder from RtpSender::subscribe_target_bitrate():

let mut rx = sender.subscribe_target_bitrate().unwrap();
while let Ok(new_bps) = rx.changed().await {
    encoder.set_bitrate(*rx.borrow());
}

ICE Restart

pc.restart_ice().await?;      // rolls fresh ICE credentials (RFC 8445 §9)
let offer = pc.create_offer().await?;  // carries the new ice-ufrag/pwd

Remote-initiated restarts (peer offers new credentials) are detected and mirrored automatically. DTLS/SRTP survive across the restart.

UPnP

• enable_upnp — Auto-map ports via UPnP IGD.
• upnp_lease_duration — UPnP port mapping lease duration in seconds (default: 3600).

RTP Latching

• enable_latching — Enable dynamic remote address detection for RTP-only mode.
• probation_max_packets — Number of packets to observe before committing a latched address.

Media Capabilities

• media_capabilities — Configure audio/video/image (T.38) codecs and SCTP port via MediaCapabilities. Video presets: VideoCapability::default() (VP8), VideoCapability::vp9() / vp9_with_rtx(pt) (RFC 9628), VideoCapability::h264().
• ssrc_start — Starting SSRC value for local tracks.
• depacketizer_strategy — Pluggable per-kind depacketizer (e.g. Vp9Depacketizer for RFC 9628 VP9 reassembly).

SCTP (Data Channels)

• sctp_rto_initial, sctp_rto_min, sctp_rto_max, sctp_max_association_retransmits, sctp_receive_window, sctp_heartbeat_interval, sctp_max_heartbeat_failures, sctp_max_burst, sctp_max_cwnd

RTP Buffer

• rtp_buffer_capacity — Per-SSRC receive buffer capacity.
• buffer_drop_strategy — DropNew or DropOldest when buffer is full.

use rustrtc::{
    PeerConnection, RtcConfiguration, RtcConfigurationBuilder,
    IceServer, TransportMode, config::T38Capability,
};

// Using builder
let config = RtcConfigurationBuilder::new()
    .transport_mode(TransportMode::Rtp)
    .enable_latching(true)
    .probation_max_packets(Some(5))
    .rtp_port_range(50000, 50100)
    .enable_upnp(true)
    .ice_tcp_policy(config::IceTcpPolicy::Enabled)
    .ice_server(IceServer::new(vec!["stun:stun.l.google.com:19302"]))
    .build();

let pc = PeerConnection::new(config);

// Direct field access
let mut config = RtcConfiguration::default();
config.transport_mode = TransportMode::WebRtc;
config.enable_latching = true;
config.rtp_start_port = Some(50000);
config.rtp_end_port = Some(50100);
config.enable_upnp = true;

T.38 fax

The t38 feature provides a complete T.38 v3 terminal: IFP wire codec, UDPTL transport (with redundancy and gap recovery), a T.30 session engine (CED/DIS → DCS/TCF → CFR → page → EOP/MCF → DCN, with timers and retries), and V.21/V.27ter DSP for audio-gateway use.

use rustrtc::t38::endpoint::{FaxEndpoint, ReceiveCodec};
use rustrtc::t38::t30::{T30FaxConfig, T30Role, T30Session};

let mut session = T30Session::new(T30FaxConfig::default());
session.role = T30Role::Callee;
let endpoint = FaxEndpoint::from_socket(socket, remote, session);
endpoint.set_codec(ReceiveCodec::Wire);
let events = endpoint.run_call(60_000).await; // drives the whole fax session

spandsp interop e2e

tests/t38_spandsp_interop.rs runs real fax sessions against a spandsp-based T.38 terminal (tools/t38-peer/t38_peer.py, ctypes over the system libspandsp). Both directions are covered: rustrtc-caller→spandsp-callee (pixel-exact page verification) and spandsp-caller→rustrtc-callee.

# requires: python3 + PIL, and libspandsp (brew install spandsp)
cargo test --features t38,t38-interop --test t38_spandsp_interop

Without the t38-interop feature the tests compile to nothing; with the feature but without python3/libspandsp they skip at runtime.

Examples

You can run the examples provided in the repository.

SFU (Selective Forwarding Unit)

A multi-user video conferencing server. It receives media from each participant and forwards it to others.

1. Run the server:

   cargo run --example rustrtc_sfu
   

2. Open your browser and navigate to http://127.0.0.1:8081. Open multiple tabs/windows to simulate multiple users.

Echo Server

The echo server example demonstrates how to accept a WebRTC connection, receive data on a data channel, and echo it back. It also supports video playback if an IVF file is provided.

1. Run the server:

   cargo run --example echo_server
   

2. Open your browser and navigate to http://127.0.0.1:3000.

DataChannel Chat

A multi-user chat room using WebRTC DataChannels.

1. Run the server:

   cargo run --example datachannel_chat
   

2. Open your browser and navigate to http://127.0.0.1:3000. Open multiple tabs to chat between them.

Audio Saver

Records audio from the browser's microphone and saves it to a file (output.ulaw) on the server.

1. Run the server:

   cargo run --example audio_saver
   

2. Open your browser and navigate to http://127.0.0.1:3000. Click "Start" to begin recording.

RTP Play (FFmpeg)

Streams a video file (examples/static/output.ivf) via RTP to a UDP port, which can be played back using ffplay.

1. Run the server:

   cargo run --example rtp_play
   

2. In a separate terminal, run ffplay (requires ffmpeg installed):

   ffplay -protocol_whitelist file,udp,rtp -i examples/rtp_play.sdp
   

License

This project is licensed under the MIT License.