Hello matey, this was something that always bugged me too. I've edited the code slightly to check for DOM changes so it's a little more reliable, I also remove the previous page from history so when you click the back button you don't get stuck in a loop. It seems to garner a little more success this way. Feel free to update with this version as you see fit:

// ==UserScript==
// @name        Bing Videos redirector
// @match       https://www.bing.com/videos/riverview/*
// ==/UserScript==
(function() {
'use strict';
const regexPattern = /youtube\.com\/embed\/(.+)\?.*/;
const checkIframes = () => {
const iframes = document.getElementsByTagName('iframe');
for (let iframe of iframes) {
let match = iframe.src.match(regexPattern);
if (match && match[1]) {
let newUrl = 'https://youtu.be/' + match[1];
history.replaceState(null, null, window.location.href);
window.location.replace(newUrl);
break;
}
}
};
checkIframes();
const observer = new MutationObserver(mutations => {
mutations.forEach(mutation => {
if (mutation.addedNodes.length > 0) {
checkIframes();
}
});
});
observer.observe(document.body, {
childList: true,
subtree: true
});
})();```

Hello! Your script is awesome and way faster! I'm a newbie in javascript so this is like magic to me lol.

I will update to your version and i'll modify to add tiktok support since that's apparently also being embeded in bing videos

Also i just realized my latest version broke the whole script

Thanks for your help!