The read-only HTMLMediaElement property duration indicates the length of the element's media in seconds. 
 The read-only HTMLMediaElement property duration indicates the length of the element's media in seconds. 
 A double-precision floating-point value indicating the duration of the media in seconds. If no media data is available, the value NaN is returned. If the element's media doesn't have a known duration—such as for live media streams—the value of duration is +Infinity. 
js
const obj = document.createElement("video"); console.log(obj.duration); // NaN
| Specification | 
|---|
| HTML Standard  # dom-media-duration-dev  | 
| Desktop | Mobile | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | WebView Android | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | |
duration | 
3 | 12 | 3.5 | 9 | ≤12.1 | 3.1 | ≤37 | 18 | 4 | ≤12.1 | 3 | 1.0 | 
HTMLMediaElement.currentTime: The current playback position of the media <audio> and <video> elements
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    https://developer.mozilla.org/en-US/docs/Web/API/HTMLMediaElement/duration