Sample code for extracting audio from RTMP stream

extract-audio-from-rtmp.js

const fs = require('fs');
const path = require('path');
const {Writable, Transform} = require('stream');
const {writeData, type: {FLVFile, FLVHeader, FLVTag}} = require('@mediafish/flv');
const {createSimpleServer} = require('@mediafish/rtmp-server');

class Terminator extends Writable {
  constructor() {
    super({objectMode: true});
  }

  _write(chunk, encoding, cb) {
    setImmediate(cb);
  }
}

class AudioExtractor extends Transform {
  constructor() {
    super({objectMode: true});
    this.header = new FLVHeader({version: 1, hasAudio: true, hasVideo: false});
    this.tags = [];
  }

  _transform(obj, _, cb) {
    const {type, timestamp, data} = obj;
    if (type === 'audio') {
      this.tags.push(new FLVTag({type: FLVTag.TagType.audio, timestamp, data}));
    }
    cb(null, obj);
  }

  _flush(cb) {
    const flv = new FLVFile(this.header, this.tags);
    const byteLength = writeData(flv, null, 0);
    const buf = Buffer.alloc(byteLength);
    writeData(flv, buf, 0);
    const filePath = path.join(__dirname, 'audio.flv');
    fs.writeFile(filePath, buf, err => {
      if (err) {
        return console.error(err.stack);
      }
      console.log(`A file writen to ${filePath}`);
      cb();
    });
  }
}

createSimpleServer('/live')
.pipe(new AudioExtractor())
.on('finish', () => {
  console.log('Finish!');
})
.on('error', err => {
  console.error(err.stack);
})
.pipe(new Terminator());