是否可以在播放之前预加载整个HTML5视频源？

Question

Solution

I created a working example of the accepted answer which uses an XHR and reports loading progress through a bar.

It's available here.

https://github.com/synthecypher/full-preload

Question

I've noticed when I create a <video> element with sources and call load() it will load to about 36% and then stops unless you play() it, at which time it'll continue to load the rest of the video as it plays.

However, I want to ensure the entire video loaded before hand as it's an element in a timed exercise and if the internet connection drops during the exercise I will have to detect such an event and restart the exercise.

I assume this is a built in feature of the HTML5 media elements but is it possible to override this native functionality?

I've attempted to load the entire video source as a arraybuffer using an XMLHttpRequest which is then converted to a blob and set as the src of a <source> element in my <video> element.

This does work however, it isn't ideal as I can't report the progress of download to the user through the use of progress bar as an XHR is a syncronous operation and will cause my JavaScript to hang until a response is received. I know XHR2 now has this funtionality but I have to support IE8+ so that's not an option.

Is there an easier more elegant solution to my problem, which will report progress?

Requirements

• Need to preload the entire <video> element's <source> before playing.
• Need to report progress of the

Answer 1

If you have the source, you can pre-download the data to a blob in JavaScript and play when ready.

The following should work if the video is on your server. If not, you'll run into CORS issues.

var video = document.getElementById("Your video element id")

var url = "Some video url"

var xhr = new XMLHttpRequest();
xhr.open("GET", url, true);
xhr.responseType = "arraybuffer";

xhr.onload = function(oEvent) {

    var blob = new Blob([oEvent.target.response], {type: "video/yourvideosmimmetype"});

    video.src = URL.createObjectURL(blob);

    //video.play()  if you want it to play on load
};

xhr.onprogress = function(oEvent) {

    if (oEvent.lengthComputable) {
        var percentComplete = oEvent.loaded/oEvent.total;
        // do something with this
    }
}

xhr.send();

Answer 2

Here is a sample to preload full video using XHR . but you need to handle CORS by yourself.

var xhrReq = new XMLHttpRequest();
xhrReq.open('GET', 'yourVideoSrc', true);
xhrReq.responseType = 'blob';

xhrReq.onload = function() {
    if (this.status === 200) {
        var vid = URL.createObjectURL(this.response);
        video.src = vid;
    }
}
xhrReq.onerror = function() {
    console.log('err' ,arguments);
}
xhrReq.onprogress = function(e){
    if(e.lengthComputable) {
        var percentComplete = ((e.loaded/e.total)*100|0) + '%';
        console.log('progress: ', percentComplete);
    }
}
xhrReq.send();