Read the duration of a mp4 file nodejs

getMP4Length.js

var buff = new Buffer(100);
fs.open(file, 'r', function(err, fd) {
  fs.read(fd, buff, 0, 100, 0, function(err, bytesRead, buffer) {
    var start = buffer.indexOf(new Buffer('mvhd')) + 17;
    var timeScale = buffer.readUInt32BE(start, 4);
    var duration = buffer.readUInt32BE(start + 4, 4);
    var movieLength = Math.floor(duration/timeScale);
    
    console.log('time scale: ' + timeScale);
    console.log('duration: ' + duration);
    console.log('movie length: ' + movieLength + ' seconds');
  });
});

Love this gist. Here is my version with all the issue fixed.

const fs = require("fs").promises;

const buff = Buffer.alloc(100);
const header = Buffer.from("mvhd");

async function main() {
    const file = await fs.open("video.mp4", "r");
    const { buffer } = await file.read(buff, 0, 100, 0);

    await file.close();

    const start = buffer.indexOf(header) + 17;
    const timeScale = buffer.readUInt32BE(start);
    const duration = buffer.readUInt32BE(start + 4);

    const audioLength = Math.floor((duration / timeScale) * 1000) / 1000;

    console.log(buffer, header, start, timeScale, duration, audioLength);
}

main();

thank you very much ! please, how can we extract a part of video using buffer? for example, I have a video of 1 minute and I want to get the first 30s of it.

Thank you very much !

i use this code but it not getting correct result i user this code for getting video duration like i want to know the video is how its long its 30 seconds its 40 seconds anyone can help me

i use this code but it not getting correct result i user this code for getting video duration like i want to know the video is how its long its 30 seconds its 40 seconds anyone can help me

You probably are using the duration variable, while you should use movieLength to achieve this.

Adding on @numToStr

I ran into some files having mvhd header towards the end (ish). In that case..

const { size } = await fs.stat("video.mp4");
const buff = Buffer.alloc(size);
const { buffer } = await file.read(buff, 0, size, 0);

The first post has the wrong offset for the start variable. It should be +16 not +17.

This is my updated gist:

  const buf = Buffer.alloc(100);
  const file = await fs.open(resource);
  const { buffer } = await file.read({
    buffer: buf,
    length: 100,
    offset: 0,
    position: 0,
  });
  await file.close();
  
  const start = buffer.indexOf(Buffer.from("mvhd")) + 16;
  const timeScale = buffer.readUInt32BE(start);
  const duration = buffer.readUInt32BE(start + 4);
  const movieLength = Math.floor(duration / timeScale);