html5：在画布内显示视频

Question

是否可以将 html5 视频显示为画布的一部分？

基本上与在画布中绘制图像的方式相同。

context.drawVideo(vid, 0, 0);

谢谢！

Answer 1

var canvas = document.getElementById('canvas');
var ctx    = canvas.getContext('2d');
var video  = document.getElementById('video');

video.addEventListener('play', function () {
    var $this = this; //cache
    (function loop() {
        if (!$this.paused && !$this.ended) {
            ctx.drawImage($this, 0, 0);
            setTimeout(loop, 1000 / 30); // drawing at 30fps
        }
    })();
}, 0);

我猜上面的代码是自我解释的，如果没有在下面发表评论，我会尝试解释上面的几行代码

编辑：
这是一个在线示例，仅供您参考：)
Demo

var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
var video = document.getElementById('video');

// set canvas size = video size when known
video.addEventListener('loadedmetadata', function() {
  canvas.width = video.videoWidth;
  canvas.height = video.videoHeight;
});

video.addEventListener('play', function() {
  var $this = this; //cache
  (function loop() {
    if (!$this.paused && !$this.ended) {
      ctx.drawImage($this, 0, 0);
      setTimeout(loop, 1000 / 30); // drawing at 30fps
    }
  })();
}, 0);

<div id="theater">
  <video id="video" src="http://upload.wikimedia.org/wikipedia/commons/7/79/Big_Buck_Bunny_small.ogv" controls="false"></video>
  <canvas id="canvas"></canvas>
  <label>
    <br />Try to play me :)</label>
  <br />
</div>

Answer 2

使用画布显示视频

显示视频与显示图像大致相同。细微差别与 onload 事件有关，而且您需要每帧渲染视频，否则您只会看到一帧而不是动画帧。

下面的演示与示例有一些细微差别。静音功能（在视频下单击静音/声音以切换声音）和一些错误检查以捕获 IE9+ 和 Edge（如果它们没有正确的驱动程序）。

使答案保持最新。

user372551 之前的答案已过时（2010 年 12 月），并且使用的渲染技术存在缺陷。它使用setTimeout 和 33.333..ms 的速率，setTimeout 将舍入到 33ms，这将导致帧每两秒丢弃一次，如果视频帧速率高于 30，可能会丢弃更多帧。使用 @ 987654326@ 还将引入由于 setTimeout 无法同步到显示硬件而创建的视频剪切。

目前没有可靠的方法可以确定视频帧速率，除非您事先知道视频帧速率，否则您应该在浏览器上以可能的最大显示刷新率显示它。 60帧

给出的最佳答案是当时（6 年前）最好的解决方案，因为 requestAnimationFrame 没有得到广泛支持（如果有的话），但 requestAnimationFrame 现在是主要浏览器的标准，应该使用而不是 setTimeout减少或消除掉帧，并防止剪切。

示例演示。

加载视频并将其设置为循环播放。在您单击视频之前，视频不会播放。再次单击将暂停。视频下方有一个静音/声音按钮。视频默认静音。

注意 IE9+ 和 Edge 的用户。您可能无法播放视频格式 WebM，因为它需要额外的驱动程序才能播放视频。可以在 tools.google.com Download IE9+ WebM support

找到它们

// This code is from the example document on stackoverflow documentation. See HTML for link to the example.
// This code is almost identical to the example. Mute has been added and a media source. Also added some error handling in case the media load fails and a link to fix IE9+ and Edge support.
// Code by Blindman67.


// Original source has returns 404
// var mediaSource = "http://video.webmfiles.org/big-buck-bunny_trailer.webm";
// New source from wiki commons. Attribution in the leading credits.
var mediaSource = "http://upload.wikimedia.org/wikipedia/commons/7/79/Big_Buck_Bunny_small.ogv"

var muted = true;
var canvas = document.getElementById("myCanvas"); // get the canvas from the page
var ctx = canvas.getContext("2d");
var videoContainer; // object to hold video and associated info
var video = document.createElement("video"); // create a video element
video.src = mediaSource;
// the video will now begin to load.
// As some additional info is needed we will place the video in a
// containing object for convenience
video.autoPlay = false; // ensure that the video does not auto play
video.loop = true; // set the video to loop.
video.muted = muted;
videoContainer = {  // we will add properties as needed
     video : video,
     ready : false,   
};
// To handle errors. This is not part of the example at the moment. Just fixing for Edge that did not like the ogv format video
video.onerror = function(e){
    document.body.removeChild(canvas);
    document.body.innerHTML += "<h2>There is a problem loading the video</h2><br>";
    document.body.innerHTML += "Users of IE9+ , the browser does not support WebM videos used by this demo";
    document.body.innerHTML += "<br><a href='https://tools.google.com/dlpage/webmmf/'> Download IE9+ WebM support</a> from tools.google.com<br> this includes Edge and Windows 10";
    
 }
video.oncanplay = readyToPlayVideo; // set the event to the play function that 
                                  // can be found below
function readyToPlayVideo(event){ // this is a referance to the video
    // the video may not match the canvas size so find a scale to fit
    videoContainer.scale = Math.min(
                         canvas.width / this.videoWidth, 
                         canvas.height / this.videoHeight); 
    videoContainer.ready = true;
    // the video can be played so hand it off to the display function
    requestAnimationFrame(updateCanvas);
    // add instruction
    document.getElementById("playPause").textContent = "Click video to play/pause.";
    document.querySelector(".mute").textContent = "Mute";
}

function updateCanvas(){
    ctx.clearRect(0,0,canvas.width,canvas.height); 
    // only draw if loaded and ready
    if(videoContainer !== undefined && videoContainer.ready){ 
        // find the top left of the video on the canvas
        video.muted = muted;
        var scale = videoContainer.scale;
        var vidH = videoContainer.video.videoHeight;
        var vidW = videoContainer.video.videoWidth;
        var top = canvas.height / 2 - (vidH /2 ) * scale;
        var left = canvas.width / 2 - (vidW /2 ) * scale;
        // now just draw the video the correct size
        ctx.drawImage(videoContainer.video, left, top, vidW * scale, vidH * scale);
        if(videoContainer.video.paused){ // if not playing show the paused screen 
            drawPayIcon();
        }
    }
    // all done for display 
    // request the next frame in 1/60th of a second
    requestAnimationFrame(updateCanvas);
}

function drawPayIcon(){
     ctx.fillStyle = "black";  // darken display
     ctx.globalAlpha = 0.5;
     ctx.fillRect(0,0,canvas.width,canvas.height);
     ctx.fillStyle = "#DDD"; // colour of play icon
     ctx.globalAlpha = 0.75; // partly transparent
     ctx.beginPath(); // create the path for the icon
     var size = (canvas.height / 2) * 0.5;  // the size of the icon
     ctx.moveTo(canvas.width/2 + size/2, canvas.height / 2); // start at the pointy end
     ctx.lineTo(canvas.width/2 - size/2, canvas.height / 2 + size);
     ctx.lineTo(canvas.width/2 - size/2, canvas.height / 2 - size);
     ctx.closePath();
     ctx.fill();
     ctx.globalAlpha = 1; // restore alpha
}    

function playPauseClick(){
     if(videoContainer !== undefined && videoContainer.ready){
          if(videoContainer.video.paused){                                 
                videoContainer.video.play();
          }else{
                videoContainer.video.pause();
          }
     }
}
function videoMute(){
    muted = !muted;
	if(muted){
         document.querySelector(".mute").textContent = "Mute";
    }else{
         document.querySelector(".mute").textContent= "Sound on";
    }


}
// register the event
canvas.addEventListener("click",playPauseClick);
document.querySelector(".mute").addEventListener("click",videoMute)

body {
    font :14px  arial;
    text-align : center;
    background : #36A;
}
h2 {
    color : white;
}
canvas {
    border : 10px white solid;
    cursor : pointer;
}
a {
  color : #F93;
}
.mute {
    cursor : pointer;
    display: initial;   
}

<h2>Basic Video & canvas example</h2>
<p>Code example from Stackoverflow Documentation HTML5-Canvas<br>
<a href="https://stackoverflow.com/documentation/html5-canvas/3689/media-types-and-the-canvas/14974/basic-loading-and-playing-a-video-on-the-canvas#t=201607271638099201116">Basic loading and playing a video on the canvas</a></p>
<canvas id="myCanvas" width = "532" height ="300" ></canvas><br>
<h3><div id = "playPause">Loading content.</div></h3>
<div class="mute"></div><br>
<div style="font-size:small">Attribution in the leading credits.</div><br>

画布附加功能

使用画布渲染视频为您提供了关于在 fx 中显示和混合的其他选项。下图显示了您可以使用画布获得的一些 FX。使用 2D API 提供了广泛的创意可能性。

与答案相关的图片Fade canvas video from greyscale to color

_{查看上述演示中的视频标题，了解上述图片中内容的归属。}

Answer 3

您需要更新 currentTime 视频元素，然后在画布中绘制帧。不要在视频上初始化 play() 事件。

您也可以使用 for ex。这个插件https://github.com/tstabla/stVideo

Answer 4

这是一个使用更现代的语法并且比已经提供的更简洁的解决方案：

const canvas = document.querySelector("canvas");
const ctx = canvas.getContext("2d");
const video = document.querySelector("video");

video.addEventListener('play', () => {
  function step() {
    ctx.drawImage(video, 0, 0, canvas.width, canvas.height)
    requestAnimationFrame(step)
  }
  requestAnimationFrame(step);
})

一些有用的链接：

• MDN Documentation for window.requestAnimationFrame()
• Can I use requestAnimationFrame?