Try this code. I tried using Chrome 54 with webdriver 2.53 on windows 8. Do not touch the mouse during the test, or even better, move the cursor out of the screen range when starting the test.
WebElement elem = driver.findElement(By.className("ytp-progress-bar"));
int width = elem.getSize().getWidth();
Actions act = new Actions(driver);
act.moveToElement(elem).moveByOffset((width/2)-2, 0).click().perform();
You can find the offset from many attributes in the div 'ytp-progress-bar'. You do not need to look for width, etc.
First you must go to the progress bar, because it disappears after 2-3 seconds due to inactivity on the video screen.
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