<video id="foo" src="foo.mp4"></video>


var vid = document.getElementById("foo");
vid.videoHeight; // returns the intrinsic height of the video
vid.videoWidth; // returns the intrinsic width of the video

Spec: https://html.spec.whatwg.org/multipage/embedded-content.html#the-video-element

Listen for the loadedmetadata event which is dispatched when the user agent has just determined the duration and dimensions of the media resource

Section 4.7.10.16 Event summary

https://www.w3.org/TR/html5/semantics-embedded-content.html#eventdef-media-loadedmetadata

videoTagRef.addEventListener('loadedmetadata', function(e){
console.log(videoTagRef.videoWidth, videoTagRef.videoHeight);
});

It should be noted that the currently accepted solution above by Sime Vidas doesn't actually work in modern browsers since the videoWidth and videoHeight properties aren't set until after the "loadedmetadata" event has fired.

If you happen to query for those properties far enough after the VIDEO element is rendered it may sometimes work, but in most cases this will return values of 0 for both properties.

To guarantee that you're getting the correct property values you need to do something along the lines of:

var v = document.getElementById("myVideo");
v.addEventListener( "loadedmetadata", function (e) {
var width = this.videoWidth,
height = this.videoHeight;
}, false );

NOTE: I didn't bother accounting for pre-9 versions of Internet Explorer which use attachEvent instead of addEventListener since pre-9 versions of that browser don't support HTML5 video, anyway.

Ready-to-use function

Here's a ready to use function which returns the dimensions of a video asynchrously, without changing anything in the document.

// ---- Definitions ----- //


/**
Returns the dimensions of a video asynchrounsly.
@param {String} url Url of the video to get dimensions from.
@return {Promise<{width: number, height: number}>} Promise which returns the dimensions of the video in 'width' and 'height' properties.
*/
function getVideoDimensionsOf(url){
return new Promise(resolve => {
// create the video element
const video = document.createElement('video');


// place a listener on it
video.addEventListener( "loadedmetadata", function () {
// retrieve dimensions
const height = this.videoHeight;
const width = this.videoWidth;


// send back result
resolve({height, width});
}, false);


// start download meta-datas
video.src = url;
});
}




// ---- Use ---- //
getVideoDimensionsOf("https://www.w3schools.com/html/mov_bbb.mp4")
.then(console.log);

Here's the video used for the snippet if you wish to see it : Big Buck Bunny

In Vuejs I use following code in mounted tag.

var app = new Vue({
el: '#id_homepage',
mounted: function () {
var v = document.getElementById("id_video");
var width = v.offsetWidth;
v.height = Math.floor(width*(9/16)); // dynamically setting video height to maintain aspect ratio
},
});

This is how it can be done in Vue:

<template>
<div>
<video src="video.mp4" @loadedmetadata="getVideoDimensions"></video>
</div>
</template>


<script>
export default {
methods: {
getVideoDimensions (e) {
console.log(e.target.videoHeight)
console.log(e.target.videoWidth)
}
}
}
</script>

This should also be noted
that in some cases such as HLS streams the "onmetadataloaded" does not work either.
in those cases, this solution works perfect.

var video = document.getElementById("video")
video.onplaying = function () {
var width = video.videoWidth
var height = video.videoHeight
console.log("video dimens loaded w="+width+" h="+height)
}