Document content
The XHTML document used in this article is as follows.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<style>
body {
background: black;
color:#CCCCCC;
}
#c2 {
background-image: url(foo.png);
background-repeat: no-repeat;
}
p {
float: left;
border :1px solid #444444;
padding:10px;
margin: 10px;
background:#3B3B3B;
}
</style>
<script type="text/javascript;version=1.8" src="main.js"></script>
</head>
<body onload="processor.doLoad()">
<p>
<video id="video" src="video.ogv" controls="true"/>
</p>
<p>
<canvas id="c1" width="160" height="96"/>
<canvas id="c2" width="160" height="96"/>
</p>
</body>
</html>The key parts of the above code are as follows:
1. Create two canvas elements with IDs c1 and c2 respectively. c1 is used to display the original video of the current frame, c2 is used to display the video after performing chroma-keying special effects; c2 is preloaded with a static image, which will be used to replace the background color part of the video.
2. The JavaScript code is imported from the main.js file; this script uses the features of JavaScript 1.8, so when importing the script, the version is specified in line 22.
3. When the web page is loaded, the processor.doLoad() method in main.js will run.
JavaScript code
The JS code in main.js contains three methods.
Initialize chroma-key
The doLoad() method is called when the XHTML document is initially loaded. The purpose of this method is to prepare the required variables for the chroma-key processing code and set up an event listener so that we can detect when the user starts playing the video.
doLoad: function() {
this.video = document.getElementById("video");
this.c1 = document.getElementById("c1");
this.ctx1 = this.c1.getContext("2d");
this.c2 = document.getElementById("c2");
this.ctx2 = this.c2.getContext("2d");
let self = this;
this.video.addEventListener("play", function() {
self.width = self.video.videoWidth / 2;
self.height = self.video.videoHeight / 2;
self.timerCallback();
}, false);
},This code obtains references to the video element and two canvas elements in the XHTML document, and also obtains references to the graphics context of the two canvases. These will be used when we implement the chroma-keying effect.
addEventListener() listens to the video element and is called when the user presses the play button on the video. In order to handle user playback, this code takes the width and height of the video, halves it (we will halve the size of the video when performing the chroma-keying effect), and then calls the timerCallback() method to initiate video capture and visual effects calculations .
Timer callback
The timer callback function is called when the video starts playing (when the "play" event occurs), and is then responsible for its own periodic call to implement keying special effects for each frame of video. .
timerCallback: function() {
if (this.video.paused || this.video.ended) {
return;
}
this.computeFrame();
let self = this;
setTimeout(function () {
self.timerCallback();
}, 0);
},The callback function first checks whether the video is playing; if not, the callback function does nothing and returns immediately.
Then call the computeFrame() method, which performs chroma-keying special effects on the current video frame.
The last thing the callback function does is call setTimeout() to allow it to be re-called as soon as possible. In a real environment, you might set the call frequency based on the frame rate of the video.
Processing video frame data
The computeFrame() method, as shown below, is actually responsible for grabbing the data of each frame and executing chroma-keying special effects.
computeFrame: function() {
this.ctx1.drawImage(this.video, 0, 0, this.width, this.height);
let frame = this.ctx1.getImageData(0, 0, this.width, this.height);
let l = frame.data.length / 4;
for (let i = 0; i < l; i++) {
let r = frame.data[i * 4 + 0];
let g = frame.data[i * 4 + 1];
let b = frame.data[i * 4 + 2];
if (g > 100 && r > 100 && b < 43)
frame.data[i * 4 + 3] = 0;
}
this.ctx2.putImageData(frame, 0, 0);
return;
}When it is called, the video element will display the most recent video frame data as follows:
In line 2, the video frame is Copied into the graphics context of the first canvas ctx1, specify the height and width values as half the frame size we saved earlier. Note that you can draw the current video frame by passing the video element to the drawImage() method of the drawing context. The result is:
The third line of code obtains a copy of the original image data of the current video frame by calling the getImageData() method of the first canvas context. It provides raw 32-bit pixel image data so we can manipulate it. Line 4 of code calculates the total number of pixels in the image by dividing the total length of the frame image data by 4.
Line 6 of code scans all pixels in a loop, obtains the red, green, and blue values of each pixel, and compares it with the predefined background color. These background colors will use the background image imported in foo.png replace.
For each pixel that is detected as background, its alpha value is replaced with zero, indicating that the pixel is completely transparent. As a result, the background portion of the final image is 100% transparent, so that when it is drawn into the context of the target on line 13, the effect is that the content is superimposed on the static background.
The resulting image looks like this:
# Do this repeatedly while the video plays, so that frame by frame is processed, rendering the chroma -Key special effects.
For more HTML5: Using Canvas to process Video in real time, please pay attention to the PHP Chinese website!
html5的div一行可以放两个吗Apr 25, 2022 pm 05:32 PMhtml5的div元素默认一行不可以放两个。div是一个块级元素，一个元素会独占一行，两个div默认无法在同一行显示；但可以通过给div元素添加“display：inline;”样式，将其转为行内元素，就可以实现多个div在同一行显示了。
html5中列表和表格的区别是什么Apr 28, 2022 pm 01:58 PMhtml5中列表和表格的区别：1、表格主要是用于显示数据的，而列表主要是用于给数据进行布局；2、表格是使用table标签配合tr、td、th等标签进行定义的，列表是利用li标签配合ol、ul等标签进行定义的。
html5怎么让头和尾固定不动Apr 25, 2022 pm 02:30 PM固定方法：1、使用header标签定义文档头部内容，并添加“position:fixed;top:0;”样式让其固定不动；2、使用footer标签定义尾部内容，并添加“position: fixed;bottom: 0;”样式让其固定不动。
HTML5中画布标签是什么May 18, 2022 pm 04:55 PMHTML5中画布标签是“<canvas>”。canvas标签用于图形的绘制，它只是一个矩形的图形容器，绘制图形必须通过脚本（通常是JavaScript）来完成；开发者可利用多种js方法来在canvas中绘制路径、盒、圆、字符以及添加图像等。
html5中不支持的标签有哪些Mar 17, 2022 pm 05:43 PMhtml5中不支持的标签有：1、acronym，用于定义首字母缩写，可用abbr替代；2、basefont，可利用css样式替代；3、applet，可用object替代；4、dir，定义目录列表，可用ul替代；5、big，定义大号文本等等。
html5废弃了哪个列表标签Jun 01, 2022 pm 06:32 PMhtml5废弃了dir列表标签。dir标签被用来定义目录列表，一般和li标签配合使用，在dir标签对中通过li标签来设置列表项，语法“<dir><li>列表项值</li>...</dir>”。HTML5已经不支持dir，可使用ul标签取代。
html5是什么意思Apr 26, 2021 pm 03:02 PMhtml5是指超文本标记语言（HTML）的第五次重大修改，即第5代HTML。HTML5是Web中核心语言HTML的规范，用户使用任何手段进行网页浏览时看到的内容原本都是HTML格式的，在浏览器中通过一些技术处理将其转换成为了可识别的信息。HTML5由不同的技术构成，其在互联网中得到了非常广泛的应用，提供更多增强网络应用的标准机。
Html5怎么取消td边框May 18, 2022 pm 06:57 PM3种取消方法：1、给td元素添加“border:none”无边框样式即可，语法“td{border:none}”。2、给td元素添加“border:0”样式，语法“td{border:0;}”，将td边框的宽度设置为0即可。3、给td元素添加“border:transparent”样式，语法“td{border:transparent;}”，将td边框的颜色设置为透明即可。
Hot AI Tools
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Undress AI Tool
Undress images for free
Clothoff.io
AI clothes remover
AI Hentai Generator
Generate AI Hentai for free.
Hot Article
Hot Tools
ZendStudio 13.5.1 Mac
Powerful PHP integrated development environment
SAP NetWeaver Server Adapter for Eclipse
Integrate Eclipse with SAP NetWeaver application server.
EditPlus Chinese cracked version
Small size, syntax highlighting, does not support code prompt function
DVWA
Damn Vulnerable Web App (DVWA) is a PHP/MySQL web application that is very vulnerable. Its main goals are to be an aid for security professionals to test their skills and tools in a legal environment, to help web developers better understand the process of securing web applications, and to help teachers/students teach/learn in a classroom environment Web application security. The goal of DVWA is to practice some of the most common web vulnerabilities through a simple and straightforward interface, with varying degrees of difficulty. Please note that this software
Atom editor mac version download
The most popular open source editor
