documentation/Always-use-"local"-to-proxy-video-through-the-server-without-creating-an-account.md

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Than add the following script in ViolentMonkey. It will always add &local=true to the end of the video URL.

// ==UserScript==
// @name        Invidious Proxy automatically
// @match       *://*.invidio.us/watch?v=*
// @run-at      document-start
// @grant       none
// ==/UserScript==


if (!(/[?&]local=/).test(location.search) && !(/[?&]quality=dash/).test(location.search)) {
  location.search += (location.search ? "&" : "?") + "local=true";
}

You can also enable this by checking Proxy videos? in your preferences.