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.
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:
And here is the test tag without preload attribute:
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.