Hearing the distorted Voice In external Media

Asterisk Asterisk APIs
1

Hi Team,
As I am trying to send the rtp back to the asterisk with the help of dgram package of node js
and i have used

channel.externalMedia({
        channelId      : uniqueIdGeneratorV4(),
        app            : ``,
        external_host  : `${rtpDetails.rtpIp}:${rtpDetails.rtpPort}`,
        format         : "slin16",
        transport      : "udp",
        encapsulation  : "rtp",
        connection_type: "client",
        direction      : "both",
    });

and on my script i am using dummy script in which i passes the external media port
and that script is streaming mp3 file to the slin16 port here is my current script

import fs from 'fs';
import dgram from 'dgram';
import prism from 'prism-media';

// === CONFIG ===
const DEST_IP = 'ASTERISK IP';                // Asterisk IP
const DEST_PORT = parseInt(process.argv[2], 10) || 10320;
const INPUT_FILE = 'input.mp3';
const SAMPLE_RATE = 16000;
const FRAME_DURATION_MS = 20;
const FRAME_SIZE = SAMPLE_RATE * FRAME_DURATION_MS / 1000; // 320 samples
const CHUNK_SIZE = FRAME_SIZE * 2;                         // 640 bytes
const PAYLOAD_TYPE = 118;
const SSRC = 0x12345678;

let sequenceNumber = 0;
let timestamp = 0;
const socket = dgram.createSocket('udp4');
let buffer = Buffer.alloc(0);
let interval = null;

// RTP header generator
function createRTPHeader(seq, ts, ssrc, marker = false) {
    const header = Buffer.alloc(12);
    header[0] = 0x80;
    header[1] = (marker ? 0x80 : 0x00) | (PAYLOAD_TYPE & 0x7F);
    header.writeUInt16BE(seq, 2);
    header.writeUInt32BE(ts, 4);
    header.writeUInt32BE(ssrc, 8);
    return header;
}

// FFmpeg decoder: MP3 → s16be (PCM big-endian, mono, 16kHz)
const decoder = new prism.FFmpeg({
    args: [
        '-i', INPUT_FILE,
        '-f', 's16be',                // Big-endian PCM
        '-acodec', 'pcm_s16be',       // Explicit codec
        '-ac', '1',                   // Mono
        '-ar', SAMPLE_RATE.toString(),
        '-loglevel', 'quiet'
    ]
});

// Handle decoded data
decoder.on('data', (chunk) => {
    buffer = Buffer.concat([buffer, chunk]);

    if (!interval) {
        interval = setInterval(() => {
            if (buffer.length >= CHUNK_SIZE) {
                const audioChunk = buffer.slice(0, CHUNK_SIZE);
                buffer = buffer.slice(CHUNK_SIZE);

                const rtpHeader = createRTPHeader(sequenceNumber, timestamp, SSRC, sequenceNumber === 0);
                const packet = Buffer.concat([rtpHeader, audioChunk]);

                socket.send(packet, 0, packet.length, DEST_PORT, DEST_IP, (err) => {
                    if (err) console.error('Send error:', err);
                });

                sequenceNumber = (sequenceNumber + 1) & 0xFFFF;
                timestamp += FRAME_SIZE;
            } else if (decoder.readableEnded && buffer.length === 0) {
                clearInterval(interval);
                socket.close();
                console.log('✅ Finished streaming.');
            }
        }, FRAME_DURATION_MS);
    }
});

decoder.on('end', () => decoder.destroy());
decoder.on('error', (err) => {
    console.error('Decoder error:', err.message);
    process.exit(1);
});

console.log(`🎵 Streaming '${INPUT_FILE}' to ${DEST_IP}:${DEST_PORT} as L16/16000/1 (PT=${PAYLOAD_TYPE})...`);
fs.createReadStream(INPUT_FILE).pipe(decoder);

Can you help me am i doing any thing wrong when i run this script i play onyl the silence no audio

i am dicy about the payload type how can i fix this please help me though it

when i use

format: "ulaw"

in external media and
in my current script when used the

const DEST_IP = 'ASTERISK IP';                // Asterisk IP
const DEST_PORT = parseInt(process.argv[2], 10) || 10320;
const INPUT_FILE = 'input.mp3';
const SAMPLE_RATE = 8000;
const FRAME_DURATION_MS = 20;
const FRAME_SIZE = SAMPLE_RATE * FRAME_DURATION_MS / 1000; // 320 samples
const CHUNK_SIZE = FRAME_SIZE * 2;                         // 640 bytes
const PAYLOAD_TYPE = 0;
const SSRC = 0x12345678;

it works but my aim to support the slin16 and other formats to play the sound please help me out through this

2

Payload type 0 is G.711 (probably µ-law), which has one byte samples. I would have thought chunk size should be 1, or the payload type is wrong.

3

Hi @david551 , for ulaw i already told that it is working fine , i want to play the slin16 audio and for that my current script i have already mentioned above

import prism from ‘prism-media’;

// === CONFIG ===
const DEST_IP = ‘ASTERISK IP’; // Asterisk IP
const DEST_PORT = parseInt(process.argv[2], 10) || 10320;
const INPUT_FILE = ‘input.mp3’;
const SAMPLE_RATE = 16000;
const FRAME_DURATION_MS = 20;
const FRAME_SIZE = SAMPLE_RATE * FRAME_DURATION_MS / 1000; // 320 samples
const CHUNK_SIZE = FRAME_SIZE * 2; // 640 bytes
const PAYLOAD_TYPE = 118;
const SSRC = 0x12345678;

4

Hi if any one can please help me up with this