Preload. If you want the video to load automatically as soon as the page loads (rather than waiting for the user to press the Play button), add a preload attribute. e.g., <video … preload> This doesn’t start playing the video automatically, it just loads it automatically. If you want to prevent the video from loading automatically, use the attribute preload=“none“. You might prefer that to save on bandwidth, if you don’t expect all your visitors to watch the video. If you don’t specify the preload attribute, what’s the default? Ask your browser maker. The default for preload is ON in Safari, but when you set it to none, the video placeholder on the page says „Loading…“ when you load the page, forever, even though it’s not really loading anything.

via The actual code to get video onto your website – & tags.