Amplify audio/video source Javascript

amplify.js

function amplify(node, gain) {
  const audioCtx = new AudioContext();
  const source = audioCtx.createMediaElementSource(node);

  // create a gain node
  const gainNode = audioCtx.createGain();
  gainNode.gain.value = gain;
  source.connect(gainNode);

  // connect the gain node to an output destination
  gainNode.connect(audioCtx.destination);
}

amplify.min.js

function amplify(node,gain){const audioCtx=new AudioContext();const source=audioCtx.createMediaElementSource(node);const gainNode=audioCtx.createGain();gainNode.gain.value=gain;source.connect(gainNode);gainNode.connect(audioCtx.destination)}

Amplify audio or video

This script was used to amplifying the audio of videos on Netflix, HBO Max, Disney+, and Amazon Prime Video. The main reason to do it by Javascript and not by browser extension is that you cast a movie to the speaker like Google Home the volume could be low.

Below you will see how to use it in the most common platforms, but obviously, this could use it for other purposes.

How to use

1. Copy the code of amplify.min.js or amplify.js.
2. Go to the platform, press ctrl + shift + i (Windows, Linux, etc) or command + Option + j or right click and select Inspect.
3. Open the tab Console and paste the code
4. Copy the code of the platform where you want to use it
5. Paste on Console and press Enter

By default the code will amplify 2 times the volume

const amplifier = 3; // Will amplify 3 times of volume
amplify(document.querySelector('video'), amplifier);

Caution: Not recommended set volume more than 5, could damage speakers or headphones.

Netflix, Disney+ and HBO Max

amplify(document.querySelector('video'));

Prime Video

const videos = document.querySelectorAll('video');
amplify(videos[videos.length - 1]);

Example in Netflix

function amplify(node, gain = 2) {
  const audioCtx = new AudioContext();
  const source = audioCtx.createMediaElementSource(node);

  // create a gain node
  const gainNode = audioCtx.createGain();
  gainNode.gain.value = gain;
  source.connect(gainNode);

  // connect the gain node to an output destination
  gainNode.connect(audioCtx.destination);
}
amplify(document.querySelector('video'));

Nice work @matiaslopezd
However, if the line amplify(document.querySelector('video')); gets executed more than one time it will generate an error saying,

Uncaught InvalidStateError: Failed to execute 'createMediaElementSource' on 'AudioContext': HTMLMediaElement already connected previously to a different MediaElementSourceNode.

We can work around the issue by tweaking the function a bit.

function amplify(node, gain = 2) {
  // Reuse existing AudioContext if available
  if (!node._audioCtx) {
    node._audioCtx = new AudioContext();
    node._sourceNode = node._audioCtx.createMediaElementSource(node);
    node._gainNode = node._audioCtx.createGain();

    node._sourceNode.connect(node._gainNode);
    node._gainNode.connect(node._audioCtx.destination);
  }

  // Just update gain
  node._gainNode.gain.value = gain;
}

With the updated code in place, the volume can be adjusted dynamically at any time by invoking the function in the browser console.
e.g.

amplify(document.querySelector('video'), 2); // increase 
amplify(document.querySelector('video'), 0.5); // decrease

@Saiful-Islam-Sakib thank you! I wrote this before I discovered the extension Volume Master. In my opinion, just use the extension 😄

@Saiful-Islam-Sakib thank you! I wrote this before I discovered the extension Volume Master. In my opinion, just use the extension 😄

There's no doubt the extension is great, but I prefer using the code instead I’d rather not have any extensions running in the background 😅
Btw thanks.