HTML5 Preload Attribute


 

This table lists the preload behavior of HTML5 browsers, at different settings of the preload attribute. We tested against the following expectations:

  • If the preload attribute is set to none, the video is not fetched before a user starts playback, resulting in less data usage but slower startup.
  • If the preload attribute is omitted, the first part of the video is fetched on page load, resulting in instant playback when the user starts. Browsers should not pre-fetch the entire video.

See the HTML5 preload spec for more details.

BROWSER PRELOAD=NONE (NO DATA) PRELOAD OMITTED (FAST START)
Firefox for Desktop 20+ 20+
Chrome for Desktop 20+ 20+
Safari for Mac 5+ 5+
Internet Explorer for Windows 10+ 1 10+ 1
Opera for Desktop 12+ 12+
Safari for iOS 3+ 2
Stock Browser for Android 4.0+ 2
Chrome for Android 30+ 2
Internet Explorer for WinPhone 7.5+ 2
Firefox for Android 20+ 2

IE9 always pre-fetches the entire video, regardless of the preload setting.

Mobile browsers never pre-fetch video data, regardless of the preload setting.

Test Setup


 

Our test video is 15:00 at 270p. For Firefox and Opera, we use this encode (WebM, 75MB). For the other browsers and devices, we use this encode (MP4 75MB). Here is the tag with preload=none attribute:

Your browser does not support HTML5 video.

 

 

And here is the test tag without preload attribute:

Your browser does not support HTML5 video.

 

 

For obtaining data, proxy your browser through a tool like the Charles web proxy:

Chrome, Firefox, Internet Explorer and Safari are automatically proxied by Charles.

iOS, Android and WinPhone have proxy options in their WiFi settings.