问题
I am trying to load a large video into a tag using XMLHttpRequest. I've successfully gotten this to work with small video files using the following code:
window.URL = window.URL || window.webkitURL;
var xhr = new XMLHttpRequest();
xhr.open('GET', 'quicktest.mp4', true);
xhr.responseType = 'blob';
xhr.onload = function(e) {
var video = document.createElement('video');
video.src = window.URL.createObjectURL(this.response);
video.autoplay = true;
document.body.appendChild(video);
};
xhr.send();
No problem if the video is small. However, my file is quite large and creates an out-of-memory error, causing Chrome to crash. Firefox won't even finish loading it, either. I've seen two seperate instances after hours of searching of people suggesting to 'download the file in chunks' and put them back together before sending it to the tag, and I've even found one very promising solution that deals with this very exact scenario. However, I'm at a complete loss as to implementing this workaround. If someone could point me in the right direction.. what would be required to impliment this fix, or anything, I would extremely appreciate it.
If curious why I'm even bothering to load video using XHR.. I'm wanting to autoplay my large video, but Chrome always jumps the gun and starts playing it immediately, thinking that it can play the entire thing with no problem (unreliable "canplaythrough" event) and I can't seem to find a way to get Chrome to buffer the entire video before playing. So I'm resorting to XHR, but having no luck.
回答1:
It's unfortunate that the browser needs to do so much copying in this scenario - the code does seem like it should work, since you're creating a blob URL and not a super long dataURI string. But sure enough, this method is very slow. However, there is another solution that should give you what you want without messing about with XHR.
Create a video element and set src to your mp4 (or webm for firefox) file. Add a listener for the 'progress' event, which should fire regularly as the browser downloads the file. In that listener, you can check the buffered property to see how much of the video has downloaded and make your own decision as to whether you're ready to start playing.
Now, here it gets a little bit ugly. Even with preload, the browser still will only buffer a little bit of the video, probably about the same amount that it needs to fire canplaythrough. You'll only get one or two progress events, and then nothing. So, when you create the video element, set it to autoplay, and then hide it and mute it. That should force the browser to download the rest of the video and trigger more progress events. When it's fully buffered, or enough to satisfy you, set currentTime back to zero, unmute and unhide.
来源：https://stackoverflow.com/questions/19645363/xmlhttprequest-to-download-large-html5-video-in-chunks