Add example for subscribe receive audio frames (#260)

* Add example for subscribe receive audio frames

* update package

* update example steps

* update package.json to use workspace dependency

* going back to using releases

* writing wav files

* update pnpm-lock.yaml

---------

Co-authored-by: lukasIO <[email protected]>

examples/publish-wav/.env.example

@@ -1,4 +1,4 @@
-# 1. Copy this file and rename it to .env.local
+# 1. Copy this file and rename it to .env
 # 2. Update the enviroment variables below.
 
 LIVEKIT_API_KEY=devkey

examples/publish-wav/package.json

@@ -12,11 +12,12 @@
   "keywords": [],
   "license": "Apache-2.0",
   "dependencies": {
-    "@livekit/rtc-node": "workspace:*",
+    "@livekit/rtc-node": "^0.7.0",
     "dotenv": "^16.4.5",
-    "livekit-server-sdk": "workspace:*"
+    "livekit-server-sdk": "^2.6.1"
   },
   "devDependencies": {
-    "@types/node": "^20.10.4"
+    "@types/node": "^20.10.4",
+    "tsx": "^4.7.1"
   }
 }

examples/receive-audio/.env.example

@@ -0,0 +1,6 @@
+# 1. Copy this file and rename it to .env
+# 2. Update the enviroment variables below.
+
+LIVEKIT_API_KEY=mykey
+LIVEKIT_API_SECRET=mysecret
+LIVEKIT_URL=wss://myproject.livekit.cloud

examples/receive-audio/README.md

@@ -0,0 +1,10 @@
+# Receive audio example
+
+This example demonstrates receiving the first audio track published in a room and writing that audio data to a wav file.
+
+To run the example:
+
+- Copy .env.example to .env and fill in the values
+- Run `pnpm install` in the root folder of this repo
+- Run `tsx index.ts` in this folder
+- From another client, join the room `test-room` and publish an audio track

examples/receive-audio/index.ts

@@ -0,0 +1,125 @@
+import { AudioStream, Room, RoomEvent, TrackKind } from '@livekit/rtc-node';
+import type { AudioFrame } from '@livekit/rtc-node/src';
+import { Buffer } from 'buffer';
+import { config } from 'dotenv';
+import * as fs from 'fs';
+import { AccessToken } from 'livekit-server-sdk';
+
+config();
+
+// Constants for WAV file
+const BITS_PER_SAMPLE = 16;
+const WAV_FILE = 'output.wav';
+
+function writeWavHeader(writer: fs.WriteStream, frame: AudioFrame) {
+  const header = Buffer.alloc(44);
+  const byteRate = (frame.sampleRate * frame.channels * BITS_PER_SAMPLE) / 8;
+  const blockAlign = (frame.channels * BITS_PER_SAMPLE) / 8;
+
+  writer = fs.createWriteStream(WAV_FILE);
+  // Write the RIFF header
+  header.write('RIFF', 0); // ChunkID
+  header.writeUInt32LE(0, 4); // ChunkSize placeholder
+  header.write('WAVE', 8); // Format
+
+  // Write the fmt subchunk
+  header.write('fmt ', 12); // Subchunk1ID
+  header.writeUInt32LE(16, 16); // Subchunk1Size (PCM)
+  header.writeUInt16LE(1, 20); // AudioFormat (PCM = 1)
+  header.writeUInt16LE(frame.channels, 22); // NumChannels
+  header.writeUInt32LE(frame.sampleRate, 24); // SampleRate
+  header.writeUInt32LE(byteRate, 28); // ByteRate
+  header.writeUInt16LE(blockAlign, 32); // BlockAlign
+  header.writeUInt16LE(16, 34); // BitsPerSample
+
+  // Write the data subchunk
+  header.write('data', 36); // Subchunk2ID
+  header.writeUInt32LE(0, 40); // Subchunk2Size placeholder
+
+  // Write the header to the stream
+  writer.write(header);
+}
+
+function updateWavHeader(path: string) {
+  // Update the size of the audio data in the header
+  const stats = fs.statSync(path);
+  const fileSize = stats.size;
+
+  const chunkSize = fileSize - 8;
+  const subchunk2Size = fileSize - 44;
+  const header = Buffer.alloc(8);
+  header.writeUInt32LE(chunkSize, 0);
+  header.writeUInt32LE(subchunk2Size, 4);
+
+  // Reopen the file for updating the header
+  const fd = fs.openSync(path, 'r+');
+  fs.writeSync(fd, header, 0, 4, 4); // Update ChunkSize
+  fs.writeSync(fd, header, 4, 4, 40); // Update Subchunk2Size
+  fs.closeSync(fd);
+}
+
+// create access token from API credentials
+const token = new AccessToken(process.env.LIVEKIT_API_KEY, process.env.LIVEKIT_API_SECRET, {
+  identity: 'example-participant',
+});
+token.addGrant({
+  room: 'test-room',
+  roomJoin: true,
+  roomCreate: true,
+  canPublish: true,
+  canPublishData: true,
+});
+const jwt = await token.toJwt();
+
+// set up room
+const room = new Room();
+
+let trackToProcess: string | null = null;
+let writer: fs.WriteStream | null = null;
+
+room.on(RoomEvent.TrackSubscribed, (track, publication, participant) => {
+  console.log('subscribed to track', track.sid, publication, participant.identity);
+  if (track.kind === TrackKind.KIND_AUDIO) {
+    const stream = new AudioStream(track);
+    trackToProcess = track.sid;
+
+    stream.on('frameReceived', (ev) => {
+      if (!trackToProcess) {
+        return;
+      }
+
+      if (writer == null) {
+        // create file on first frame
+        // also guard when track is unsubscribed
+        writer = fs.createWriteStream('output.wav');
+        writeWavHeader(writer, ev.frame);
+      }
+
+      if (writer) {
+        const buf = Buffer.from(ev.frame.data.buffer);
+        writer.write(buf);
+      }
+    });
+  }
+});
+
+const finishedPromise = new Promise<void>((resolve) => {
+  room.on(RoomEvent.TrackUnsubscribed, (_, publication, participant) => {
+    console.log('unsubscribed from track', publication.sid, participant.identity);
+    if (publication.sid === trackToProcess) {
+      trackToProcess = null;
+      if (writer) {
+        writer.close();
+        // update header
+        updateWavHeader(WAV_FILE);
+      }
+      resolve();
+    }
+  });
+});
+
+await room.connect(process.env.LIVEKIT_URL, jwt, { autoSubscribe: true, dynacast: true });
+console.log('connected to room', room);
+
+// stay in the room until publisher leaves
+await finishedPromise;

examples/receive-audio/package.json

@@ -0,0 +1,22 @@
+{
+  "name": "example-receive-audio",
+  "author": "LiveKit",
+  "private": "true",
+  "description": "",
+  "type": "module",
+  "main": "index.ts",
+  "scripts": {
+    "lint": "eslint -f unix \"**/*.ts\""
+  },
+  "keywords": [],
+  "license": "Apache-2.0",
+  "dependencies": {
+    "@livekit/rtc-node": "^0.7.0",
+    "dotenv": "^16.4.5",
+    "livekit-server-sdk": "^2.6.1"
+  },
+  "devDependencies": {
+    "@types/node": "^20.10.4",
+    "tsx": "^4.7.1"
+  }
+}