<video> and onloadedmetadata-event

问题

I'd like to use the dimensions of a HTML5 video element in JavaScript. The video-tag itself does not have any dimensions set, so I expect it to scale to the size of the video (which it does). My markup looks like this:

<video id="viddy" autoplay>
<source src="myvideo.mp4" type='video/mp4; codecs="avc1.42E01E"' />
</video>

When I just use jQuery to get the element's height() and/or width() I will get a default value of 300 as it will not wait for the video to load. So what I found out on the web (here and here) is that I should be waiting for the onloadedmetadata-event. So I am trying to do the following in my JS:

var video = document.getElementById('viddy');
video.onloadedmetadata = function(e){
var dimensions = [video.videoWidth, video.videoHeight];
alert(dimensions);
} 

Yet, the event will never fire (although the video will load and play) and I'll never get my dimensions. Same happens with a jQuery-bind('load', and every other way I could think of. Any idea? Thanks.

回答1:

Put your code into a function at the end of your HTML head (e.g. called init) and bind it to the DOMContentLoaded event:

function init() {
    var video = document.getElementById('viddy');
    video.onloadedmetadata = function(e){
        var dimensions = [video.videoWidth, video.videoHeight];
        alert(dimensions);
    }
}

document.addEventListener("DOMContentLoaded", init, false);

<video id="viddy" autoplay>
    <source src="http://media.w3.org/2010/05/sintel/trailer.webm" type='video/webm' />
</video>

For Chrome

You should change adding the listener to:

video.addEventListener('loadedmetadata', function(e){

function init() {
    var video = document.getElementById('viddy');
    video.addEventListener('loadedmetadata', function(e){
        var dimensions = [video.videoWidth, video.videoHeight];
        alert(dimensions);
    });
}

document.addEventListener("DOMContentLoaded", init, false);

<video id="viddy" autoplay>
    <source src="http://media.w3.org/2010/05/sintel/trailer.webm" type='video/webm' />
</video>

With jQuery

$(document).ready(function() {
    $('#viddy').on('loadedmetadata', function() {
        var dimensions = [this.videoWidth, this.videoHeight];
        alert(dimensions);
    });
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/1.7.1/jquery.min.js"></script>
<video id="viddy" autoplay>
    <source src="http://media.w3.org/2010/05/sintel/trailer.webm" type='video/webm' />
</video>

来源：https://stackoverflow.com/questions/8983714/video-and-onloadedmetadata-event