Volume Booster for YouTube™ per Joe Ertaba

The Volume Booster extension is a tool designed to enhance the audio output of supported media players. Whether you're watching videos or listening to music, this extension aims to elevate your audio experience by boosting the volume level beyond the standard limitations with greater clarity and impact.

The extension installs a "2x" button next to the settings button of the YouTube player. It is disabled by default. If the user clicks the button once, the audio gain node is installed on the source node, causing the audio volume to increase level twice (200%; similar to VLC player). You can click the button once more to deactivate the boosting.

Note:
The compatibility of this extension with your audio equalizer extension may vary. Its compatibility is dependent on the method used by the equalizer to perform audio filtering, whether it is applied directly to the player (not compatible) or to the page itself (compatible).

This extension supports volume boosting with keyboard shortcuts. Read the FAQs page for more info