javascript从视频url生成视频缩略图

Question

我将从 JavaScript 中的视频网址生成视频缩略图。我需要通过 ajax 完成此操作。所以我遵循了这种方法。

var src = thumbnail; ///video url not youtube or vimeo,just video on server
var video = document.createElement('video');

video.src = src;

video.width = 360;
video.height = 240;

var canvas = document.createElement('canvas');
canvas.width = 360; 
canvas.height = 240;
var context = canvas.getContext('2d');

context.drawImage(video, 0, 0, canvas.width, canvas.height);
var dataURI = canvas.toDataURL('image/jpeg');
html += '<figure>';
html += '<img src="' + dataURI + '' + '" alt="' + item.description + '" />';
html += '<figurecaption>'+item.description+'</figurecaption>'
html += '</figure>';

但我得到的只是黑色图像。我猜是因为负载问题，但找不到解决方案。期待您的来信。

问候。

Answer 1

But what I get is just black image. I guess it's because load problem but can't find a solution. Looking forward to hearing from you.

这可能是因为您调用时尚未加载任何帧:

context.drawImage(video, 0, 0, canvas.width, canvas.height);

您应该在收到一些“loadeddata”事件后执行此操作(检查 https://developer.mozilla.org/en-US/docs/Web/Events/loadeddata )

所以你的代码将变成:

var src = thumbnail; ///video url not youtube or vimeo,just video on server
var video = document.createElement('video');

video.src = src;

video.width = 360;
video.height = 240;

var canvas = document.createElement('canvas');
canvas.width = 360; 
canvas.height = 240;
var context = canvas.getContext('2d');

video.addEventListener('loadeddata', function() {
    context.drawImage(video, 0, 0, canvas.width, canvas.height);
    var dataURI = canvas.toDataURL('image/jpeg');
    html += '<figure>';
    html += '<img src="' + dataURI + '' + '" alt="' + item.description + '" />';
    html += '<figurecaption>'+item.description+'</figurecaption>'
    html += '</figure>';
});

请注意，这将是异步的，因此您可能必须更改对 html 变量的处理方式，而是设置 image.src = dataURI;，即 image 对 Image DOM 节点(您插入的节点)的引用