@blockcast/transport

Unified transport manager for MoQ with WebTransport, SSM multicast, AMT, DRIAD, and FEC support.

Features

• Transport Hierarchy: Automatic fallback from native SSM → IGMP → AMT → DRIAD → MOQ
• Adaptive Bitrate: Progressive quality upgrade based on network conditions
• FEC Recovery: RaptorQ-based forward error correction for lossy paths
• A/V Sync: SharedClock for cross-track synchronization
• DRIAD Discovery: RFC 8777 relay discovery via DNS-over-HTTPS

Installation

pnpm add @blockcast/transport

Usage

Basic SSM Transport

import { ssmTransport } from '@blockcast/transport';

// Set up callbacks
ssmTransport.setPacketCallback((data) => {
  console.log('Received packet:', data.byteLength, 'bytes');
});

ssmTransport.setStateCallback((state) => {
  console.log('Transport state:', state.mode, state.connected);
});

// Connect to multicast stream
await ssmTransport.connect({
  group: '232.1.1.1',
  source: '192.168.1.100',
  port: 5000,
  streamType: 'video',
  driadEnabled: true,
});

// Get current state
const state = ssmTransport.getState();
console.log(`Mode: ${state.mode}, Packets: ${state.packetsReceived}`);

// Disconnect
ssmTransport.disconnect();

With FEC Recovery

import { MmtFecClient, createMulticastFecHandler } from '@blockcast/transport/fec';

// Create FEC client
const fecClient = new MmtFecClient({
  interleaveDepth: 30,
  blockTimeoutMs: 2000,
  greenFillEnabled: true,
  onMfuReady: (mfu) => {
    console.log('MFU ready:', mfu.mpuSequenceNumber);
    if (mfu.recoveredViaFec) {
      console.log('Recovered via FEC!');
    }
  },
});

// Set WASM module (from libmmt)
fecClient.setWasmModule(mmtWasmModule);
await fecClient.init();

// Create packet handler for window.Multicast
const handler = createMulticastFecHandler(fecClient);
window.Multicast.subscribeSSM({
  group: '232.1.1.1',
  source: '192.168.1.100',
  port: 5000,
}).then(sub => {
  sub.onpacket = (event) => handler(event.data);
});

A/V Synchronization

import { getSharedClock } from '@blockcast/transport/clock';

const clock = getSharedClock();

// Set anchor on first keyframe
clock.setAnchor(firstFrame.timestamp);

// Check if frame should be rendered
const decision = clock.shouldRender(frame.timestamp);
if (decision === 'render') {
  renderFrame(frame);
} else if (decision === 'hold') {
  const waitMs = clock.getWaitTimeMs(frame.timestamp);
  await sleep(waitMs);
  renderFrame(frame);
} else {
  // discard - frame is too late
  frame.close();
}

DRIAD Discovery

import { driadDiscovery } from '@blockcast/transport';

// Discover AMT relays for a multicast group
const relays = await driadDiscovery.discoverRelays('232.1.1.1');
const bestRelay = await driadDiscovery.selectBestRelay(relays);

console.log(`Best relay: ${bestRelay.host}:${bestRelay.port} (RTT: ${bestRelay.rtt}ms)`);

Direct AMT Gateway

import { AMTGateway } from '@blockcast/transport';

const gateway = new AMTGateway({
  relayAddress: 'amt-relay.example.com',
  relayPort: 2268,
  onPacket: (packet) => {
    console.log('Received:', packet.data.length, 'bytes from', packet.srcAddress);
  },
  onStateChange: (newState, oldState) => {
    console.log(`State: ${oldState} -> ${newState}`);
  },
});

// Join multicast group
await gateway.joinGroup('232.1.1.1', 5000, '192.168.1.100');
await gateway.open();

// Later...
await gateway.close();

Quality Levels

The adaptive bitrate controller supports these quality levels:

| Name | Bitrate | Resolution | FPS | |------|---------|------------|-----| | 240p | 300 Kbps | 426x240 | 15 | | 360p | 500 Kbps | 640x360 | 24 | | 480p | 1 Mbps | 854x480 | 30 | | 720p | 2.5 Mbps | 1280x720 | 30 | | 1080p | 5 Mbps | 1920x1080 | 30 | | 1440p | 8 Mbps | 2560x1440 | 30 | | 4K | 15 Mbps | 3840x2160 | 30 |

Transport Modes

| Mode | Description | Requirements | |------|-------------|--------------| | ssm | Native Source-Specific Multicast | IWA + Direct Sockets | | igmp | Native Any-Source Multicast | IWA + Direct Sockets | | amt | AMT Gateway (configured relay) | WebSocket or Direct Sockets | | driad | AMT via DRIAD discovery | HTTP access | | moq | MOQ WebTransport fallback | WebTransport |

License

Apache-2.0