html5:在画布中显示视频

Question

是否可以在画布中显示html5-video？

与在画布中绘制图像的方式基本相同.

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,如果不在下面发表评论,我会尝试解释上面几行代码

编辑:
这是一个在线示例,仅供您使用:)
演示

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非常相似.微小差异与onload事件有关,以及你需要每帧渲染视频的事实,或者你只能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.一个静音功能(在视频点击静音/声音开启以切换声音)和一些错误检查,以捕获IE9 +和Edge,如果他们没有正确的驱动程序.

保持最新的答案.

user372551之前的答案已过时(2010年12月),并且在使用的渲染技术方面存在缺陷.它使用setTimeout和33.333 ...的速率,其中setTimeout将向下舍入到33ms,这将导致帧每两秒丢弃一次,如果视频帧速率高于30,可能会下降更多.使用setTimeout还会引入视频剪切创建因为setTimeout无法同步到显示硬件.

目前能够确定视频的帧速率,除非你事先知道你应该在浏览器上的最大显示刷新率可能显示该视频帧速率没有可靠的方法.60fps的

给出的最佳答案是时间(6年前)最好的解决方案,requestAnimationFrame因为没有广泛支持(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来减少或删除丢帧,以及防止剪切.

示例演示.

加载视频并将其设置为循环.直到您点击它才会播放视频.再次单击将暂停.视频下方的按钮上有静音/声音.视频默认为静音.

注意IE9 +和Edge的用户.您可能无法播放视频格式WebM,因为它需要其他驱动程序才能播放视频.可以在tools.google.com 上找到它们.下载IE9 + WebM支持

// 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>

帆布附加功能

使用画布渲染视频为您提供了有关在fx中显示和混合的其他选项.下图显示了使用画布可以获得的一些FX.使用2D API可提供广泛的创作可能性.

与答案相关的图像将画布视频从灰度变为彩色

_{请参阅上面演示中的视频标题,了解上述图片中内容的归属.}

Answer 3

我想提供一个使用更现代语法的解决方案,并且比已经提供的解决方案更简洁:

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:

• window.requestAnimationFrame()的MDN文档
• 我可以使用requestAnimationFrame吗？