Solved it by doing var videotitle = document.title.split(" - YouTube")[0];

You can grab the tab title in the background.js, it will return the youtube video title

chrome.tabs.onActivated.addListener(function (activeInfo) {
chrome.tabs.get(activeInfo.tabId, function (tab) {
    console.log("Title: " + tab.title);
});

});

You can also use this line of code in the F12 developer tools:

ytInitialPlayerResponse.videoDetails.title

The same line of code should work on your extension as well.