Improved user experience, minimized incentives to install ad blockers, and reduced data consumption
Chrome's autoplay policies changed in April of 2018 and I'm here to tell
you why and how this affects video playback with sound. Spoiler
alert: users are going to love it!
New behaviors
As you may have
noticed
, web browsers are moving towards stricter autoplay
policies in order to improve the user experience, minimize incentives to install
ad blockers, and reduce data consumption on expensive and/or constrained
networks. These changes are intended to give greater control of playback to
users and to benefit publishers with legitimate use cases.
Chrome's autoplay policies are simple:
- Muted autoplay is always allowed.
- Autoplay with sound is allowed if:
- Top frames can
delegate autoplay permission
to their iframes to
allow autoplay with sound.
The Media Engagement Index (MEI) measures an individual's propensity to consume
media on a site. Chrome's approach is a ratio of visits to significant media
playback events per origin:
- Consumption of the media (audio/video) must be greater than seven seconds.
- Audio must be present and unmuted.
- The tab with the video is active.
- Size of the video (in px) must be greater than
200x140
.
From that, Chrome calculates a media engagement score, which is highest on sites
where media is played on a regular basis. When it is high enough, media is
allowed to autoplay on desktop only.
A user's MEI is available at the
about://media-engagement
internal page.
Developer switches
As a developer, you may want to change Chrome autoplay policy behavior locally
to test your website for different levels of user engagement.
You can disable the autoplay policy entirely by using a
command line
flag
:
chrome.exe --autoplay-policy=no-user-gesture-required
.
This allows you to test your website as if user were strongly engaged with
your site and playback autoplay would be always allowed.
You can also decide to make sure autoplay is never allowed by disabling MEI and
whether sites with the highest overall MEI get autoplay by default for
new users.
Do this with flags
:
chrome.exe
--disable-features=PreloadMediaEngagementData,
MediaEngagementBypassAutoplayPolicies
.
Iframe delegation
A
permissions policy
allows developers to selectively enable and disable
browser features and APIs. Once an origin has received autoplay
permission, it can delegate that permission to cross-origin iframes with the
permissions policy for autoplay
. Note that autoplay is allowed by default on
same-origin iframes.
<!-- Autoplay is allowed. -->
<iframe src="https://cross-origin.com/myvideo.html" allow="autoplay">
<!-- Autoplay and Fullscreen are allowed. -->
<iframe src="https://cross-origin.com/myvideo.html" allow="autoplay; fullscreen">
When the permissions policy for autoplay is disabled, calls to
play()
without a
user gesture will reject the promise with a
NotAllowedError
DOMException. And
the autoplay attribute will also be ignored.
Examples
Example 1:
Every time a user visits
VideoSubscriptionSite.com
on their
laptop they watch a TV show or a movie. As their media engagement score is
high, autoplay is allowed.
Example 2:
GlobalNewsSite.com
has both text and video content.
Most users go to the site for text content and watch videos only occasionally.
Users' media engagement score is low, so autoplay wouldn't be allowed if a user
navigates directly from a social media page or search.
Example 3:
LocalNewsSite.com
has both text and video content.
Most people enter the site through the homepage and then click on the news
articles. Autoplay on the news article pages would be allowed because of user
interaction with the domain. However, care should be taken to make sure users
aren't surprised by autoplaying content.
Example 4:
MyMovieReviewBlog.com
embeds an iframe with a movie trailer to
go with a review. Users interacted with the domain to get to the blog, so
autoplay is allowed. However, the blog needs to explicitly delegate that
privilege to the iframe in order for the content to autoplay.
Chrome enterprise policies
It is possible to change the autoplay behavior with Chrome enterprise policies
for use cases such as kiosks or unattended systems. Check out the
Policy
List
help page to learn how to set the autoplay related enterprise
policies:
- The
AutoplayAllowed
policy controls whether
autoplay is allowed or not.
- The
AutoplayAllowlist
policy allows you to
specify an allowlist of URL patterns where autoplay will always be enabled.
Best practices for web developers
Audio/Video elements
Here's the one thing to remember: Don't ever assume a video will play, and
don't show a pause button when the video is not actually playing. It is so
important that I'm going to write it one more time below for those who simply
skim through that post.
You should always look at the
Promise
returned by the play function to see if
it was
rejected
:
var promise = document.querySelector('video').play();
if (promise !== undefined) {
promise.then(_ => {
// Autoplay started!
}).catch(error => {
// Autoplay was prevented.
// Show a "Play" button so that user can start playback.
});
}
One cool way to engage users is to use muted autoplay and let them chose
to unmute. (See the example below.) Some websites already do this effectively,
including Facebook, Instagram, Twitter, and YouTube.
<video id="video" muted autoplay>
<button id="unmuteButton"></button>
<script>
unmuteButton.addEventListener('click', function() {
video.muted = false;
});
</script>
Events that trigger user activation are still to be defined consistently across
browsers. I'd recommend you stick to
"click"
for the time being then. See
GitHub issue whatwg/html#3849
.
Web Audio
The
Web Audio API
has been covered by autoplay since Chrome 71.
There are a few things to know about it. First, it is good practice to wait for
a user interaction before starting audio playback so that users are aware of
something happening. Think of a "play" button or "on/off" switch for instance.
You can also add an "unmute" button depending on the flow of the app.
If you create your
AudioContext
on page load, you'll have to call
resume()
at some time after the user interacted with the page (e.g., after a user clicks
a button). Alternatively, the
AudioContext
will be resumed after a user
gesture if
start()
is called on any attached node.
// Existing code unchanged.
window.onload = function() {
var context = new AudioContext();
// Setup all nodes
// ...
}
// One-liner to resume playback when user interacted with the page.
document.querySelector('button').addEventListener('click', function() {
context.resume().then(() => {
console.log('Playback resumed successfully');
});
});
You may also create the
AudioContext
only when the user interacts with the
page.
document.querySelector('button').addEventListener('click', function() {
var context = new AudioContext();
// Setup all nodes
// ...
});
To detect whether the browser requires a user interaction to play audio, check
AudioContext.state
after you've created it. If playing is allowed, it should
immediately switch to
running
. Otherwise it will be
suspended
. If you listen
to the
statechange
event, you can detect changes asynchronously.
To see an example, check out the small
Pull Request
that fixes
Web Audio playback for these autoplay policy rules for
https://airhorner.com
.