Compress audio to MP3 on the web: a guide for developers

If you build web apps that accept audio uploads, sooner or later you'll need a flow to convert and compress to MP3 with a good balance of size and quality. In this guide you'll see when to use FFmpeg on the server, when to go with ffmpeg.wasm in the browser, and which presets and bitrates work best for voice and music—especially for audio coming from WhatsApp or Telegram.

Architectures: client vs server

There are two main approaches to convert/compress audio in a web app. Choosing one or the other depends on file sizes, budget, and the compatibility you need.

Recommended quality presets

• Voice (notes, interviews): 64–128 kbps, mono optional. Good balance of clarity and size.
• Light music or voice with background: 128–160 kbps CBR or high VBR.
• Full music: 192 kbps or higher if the audience expects it.
• Ultra-light files: 64 kbps for voice when size is critical.

Code examples

FFmpeg CLI (server)

# Clear voice (mono) at 96 kbps
ffmpeg -i input.m4a -ac 1 -c:a libmp3lame -b:a 96k output.mp3

# Music at 192 kbps CBR
ffmpeg -i input.wav -c:a libmp3lame -b:a 192k output.mp3

# High-quality VBR (~170–210 kbps)
ffmpeg -i input.wav -c:a libmp3lame -q:a 2 output.mp3

Node.js (fluent-ffmpeg)

import ffmpeg from "fluent-ffmpeg";

function toMp3Voice(inputPath, outPath) {
  return new Promise((res, rej) => {
    ffmpeg(inputPath)
      .audioChannels(1)
      .audioCodec("libmp3lame")
      .audioBitrate("96k")
      .on("end", res)
      .on("error", rej)
      .save(outPath);
  });
}

Python (pydub + FFmpeg)

from pydub import AudioSegment
audio = AudioSegment.from_file("input.opus")
audio.set_frame_rate(44100).set_channels(1).export("out.mp3", format="mp3", bitrate="96k")

In the browser with ffmpeg.wasm

import { createFFmpeg, fetchFile } from "@ffmpeg/ffmpeg";
const ffmpeg = createFFmpeg({ log: false });

async function convertClientSide(file) {
  if (!ffmpeg.isLoaded()) await ffmpeg.load();
  ffmpeg.FS("writeFile", "in.m4a", await fetchFile(file));
  await ffmpeg.run("-i", "in.m4a", "-ac", "1", "-c:a", "libmp3lame", "-b:a", "96k", "out.mp3");
  const data = ffmpeg.FS("readFile", "out.mp3");
  return new Blob([data.buffer], { type: "audio/mpeg" });
}

Tip: run ffmpeg.wasm inside a Web Worker to avoid blocking the UI and show progress using ffmpeg.setProgress.

UX for mobile audio (WhatsApp/Telegram)

• “Drag & drop” button + file picker: accept="audio/*,.opus,.m4a,.aac,.ogg,.amr".
• Detect common sources: if .opus or .ogg, suggest the OPUS → MP3 guide.
• Alternate CTA for “reduce the size of an MP3” (popular query in Analytics).
• Explain bitrates in plain language and save the last choice in localStorage.

Performance, cost, and security

Frequently asked questions