# Autoplay of HTMLMediaElements Autoplay is the concept of playing media elements without user gesture. The policy that defines when autoplay is allowed is defined [here](https://www.chromium.org/audio-video/autoplay). The autoplay logic follows the [HTML spec](https://html.spec.whatwg.org/multipage/embedded-content.html#media-elements). There are two ways of initiating autoplay: * Autoplay by attribute: Setting the `autoplay` attribute on the media element. The element will try to autoplay when the `readyState` changes to HAVE_ENOUGH_DATA. * Autoplay by `play()` method: Explicitly calling the `play()` method without user gesture. All the autoplay logic is handled by the AutoplayPolicy class. When the media element wants to perform some action (like unmute, autoplay by attribute or `play()` method), it will send a request to AutoplayPolicy, and if the request is approved, the element can autoplay, otherwise it should be paused. Also the media element should inform the AutoplayPolicy about relevant changes such as "the element has been moved to a new document". ## User gesture lock Each media element has a user gesture lock. If the element is allowed to autoplay, the lock is initialized as `false`, otherwise it's `true`. When the element is trying to initate autoplay, we check the gesture lock. If the lock is `false`, it will be allowed. Otherwise autoplay will be blocked. An exception is that if the element is a muted video element, the gesture lock check will be bypassed. To unlock the gesture lock (make it `false`). The page needs to call play() or load() on the element when responding to a user gesture. ## Autoplay flowchart The treatments of autoplay by different methods are different. For autoplay by attribute, it is: ![Autoplay by attribute](autoplay_by_attribute.png) This means if autoplay is initiated by attribute, it enters the autoplaying phase, we play it as long as the video is visible. When the page explicitly calls `play()`, `pause()`, we leave the autoplaying phase. When the page tries to unmute the video, we check the gesture lock and pause the video if it is still `true`. For autoplay by `play()` method, it is: ![Autoplay by play() method](autoplay_by_play_method.png) This means if autoplay is initiated by `play()` method, we continue playing the video as normal `play()`. However if the page tries to unmute the video, we check the gesture lock and pause the video if it is still `true`.