31 Dec 2019

Mantain consistent .mp4 video compression with FFmpeg

javascript ffmpeg

So you maybe already know ffmpeg the popular library for video compression, stream, and they had many though you can check that on their website.

Recently I found nice article about compressing using FFmpeg

on that article this guy using bitrate to compress the .mp4 file. But to compress files that had size 1Mb to 10Mb that script makes it bigger ~ not make the video smaller.

I had some project that requires video compression back then I do that with scaling (cause it's faster than bitrate compression) found on this StackOverflow answer:

My old project usually uses it, but now I had a use case when I can't scale the video to maintain its original size, so after found that guy answer I just want to share some script here.

/* eslint-disable no-new */
const ffmpeg = require("fluent-ffmpeg");
const ffmpegPath = require("ffmpeg-static").path;
const ffprobePath = require("ffprobe-static").path;
const path = require("path");
const uuid = require("uuid/v3");

// video path
const videoPath = path.join(__dirname, "video", "output.mp4");
// set ffmpeg path

* Extract Metadata from a video
* @param {String} path

function metadata(path) {
return new Promise((resolve, reject) => {
ffmpeg.ffprobe(path, (err, metadata) => {
if (err) {

* FFmpeg commaand to compress video
* @param {String} input
* Path to input file
* @param {String} output
* Path to output file
* @param {Number} bitrate
* The bitrate you specify to compress video in bytes

function command(input, output, bitrate) {
return new Promise((resolve, reject) => {
"-c:v libx264",
`-b:v ${bitrate}k`,
"-c:a aac",
"-b:a 58k",
.on("start", (command) => {
console.log("TCL: command -> command", command);
.on("error", (error) => reject(error))
.on("end", () => resolve())

* Choose the right bitrate for video based on Size
* @param {Number} bytes

function whatBitrate(bytes) {
const ONE_MB = 1000000;
const BIT = 28; // i found that 28 are good point fell free to change it as you feel right
const diff = Math.floor(bytes / ONE_MB);
if (diff < 5) {
return 128;
} else {
return Math.floor(diff * BIT * 1.1);

// this compress video based on bitrate
async function compress() {
const name = uuid(videoPath, "1b671a64-40d5-491e-99b0-da01ff1f3341");
const outputPath = path.join(__dirname, "video", `${name}.mp4`);
const inputMetadata = await metadata(videoPath);
const bitrate = whatBitrate(inputMetadata.format.size);
await command(videoPath, outputPath, bitrate);
const outputMetadata = await metadata(outputPath);

return {
old_size: inputMetadata.format.size,
new_size: outputMetadata.format.size,

.then((data) => console.log(data))
.catch((err) => console.log(err));

the 28 and 1.1 are the one that works for me, you can change it, I know that my app would not handle more than 1GB so here is the list

Original Compressed Bitrate
2.1Mb 1.4Mb 128k
10.2Mb 5.6Mb 308k
51Mb 31Mb 1570k

The audio is fine though.