14 DAY TRIAL // YouTube is the largest video site on the planet and one of the biggest Internet traffic generators on the web. As such, anything it can do to optimize usage has huge effects not only on the site, but on the entire web as well.
That's how the Dynamic Adaptive Streaming over HTTP – or DASH – technology came about. The feature is responsible for serving video on YouTube and preloads only a few seconds ahead as you watch a clip.
The idea is to only serve as much data as is needed if, for example, the user closes the tab before the video finishes. Previously, the entire video, at the selected quality, was preloaded in its entirety as fast it could be downloaded.
While this is more wasteful of bandwidth and means that the video is downloaded again if you switch to 720p from 480p, for example, it is preferable in some cases. For example, if you're on a particularly slow connection and would rather wait for a significant part of the video to be preloaded before hitting play.
Thankfully, there is a way to disable the DASH feature and switch back to the old style preloading. All you need is the YouTube Center extension, available for Chrome, Firefox, Opera 12, and Maxthon.
Since the extension enables you to download videos, you won't find it in the Chrome Web Store, but you can grab it from the project's GitHub page. It's also available as a userscript, for Greasemonkey or TamperMonkey.
Once you've installed it, you'll notice a "gear" icon next to your profile controls. Click on it, go to the Player tab, and you'll find the "Dash Playback" option enabled by default. Just disable it to switch to the old preloading method.
The extension comes with plenty of other options and features, and you can look around and see if there's anything you might find useful.