driver.set_script_timeout(10)
driver.get('https://www.youtube.com/watch?v=hdw1uKiTI5c')
wait = WebDriverWait(driver, 5)
video = wait.until(EC.visibility_of_element_located((By.TAG_NAME, 'video')))
driver.execute_async_script(
    """
    var video = arguments[0],
        callback = arguments[arguments.length - 1];
    video.addEventListener('loadstart', listener);
    function listener() {
        callback();
    };
"""
    , video)
driver.execute_script('arguments[0].muted = true;', video)
How to mute all sounds in chrome webdriver with selenium