HRD Emulator in HTML5

Posted on March 21, 2012 by Moto

Just like MPEG-2 video uses VBV (Video Buffer Verifier), H.264 standard uses HRD (Hypothetical Reference Decoder) to define correctness of streams.

One of the verification provided by HRD is CPB buffer fullness. The idea is simple; feed H.264 stream to HRD and monitor the CPB fullness. Make sure the fullness never goes negative nor above the CPB buffer size. The importance of this buffer fullness requirement was explained here.

HRD defines the CPB fullness in somewhat counter intuitive way. To make it easy, I wrote an interactive HRD emulator in HTML5.

HRD Emulator (CBR)

The blue line the number of bits entered to HRD over time. The input rate is constant in CBR mode, i.e. the blue line is straight. The red line is the number of bits removed (= Decoded) from CPB. Thus, the CPB fullness is the blue line minus the red line for a given time.

Let’s select the VBR in Rate Control Mode.

HRD Emulator (VBR)

The blue line now has some periods where the input rate is zero. H.264 standard uses init_cpb_removal_delay to control the period; Bits for a picture N can enter HRD only after the picture decode time minus init_cpb_removal_delay.

To see this rule more clearly, check “Show init_cpb_removal_delay” option. When the last bit of picture N – 1 arrives before the picture N decoding time minus init_cpb_removal_delay, the input rate goes down to zero.

HRD (VBR) with init_cpb_removal_delay

The value of init_cpb_removal_delay also determines the initial decoding delay. It’s currently set to 50 ms. It means the first picture is decoded 50 ms after the first bit of the picture enters HRD.

The initial decoding delay determines the channel switching delay as discussed here. Can we reduce it to make channel switching faster?

HRD underflow due to the short initial delay

Not really. As shown above, reducing the value of init_cpb_removal_delay resulted in the underflow error (the red line crosses the blue line).

H.264 standard has introduced another parameter to allow the reduction of initial decoding delay at the expense of increased average bit rate. Here we have init_cpb_removal_delay_offset parameter. It’s added to init_cpb_removal_delay for every picture except the first one.

HRD with non-zero init_cpb_removal_delay_offset

H.264 HRD provides these parameters to encoders so that they can choose optimal bit stream configuration for each target devices.

Here are HTML and Java Script of the HRD emulator above.

<html>

<head>

<title>HRD Emulator</title>

#plot {

float : left

}

#control-container {

float : left

}

#widget {

float : right;

width : 10em

}

#heading {

float : left

}

</style>

</head>

</div>

</div>

<div class="heading">initial_cpb_removal_delay [<span id="showICRD"> </span> ms]</div>

<div>

</div>

<div class="heading">initial_cpb_removal_delay_offset [<span id="showICRDO"> </span> ms]</div>

<div>

</div>

<div>Rate Control Mode</div>

<div>

<input type="radio" name="mode" value="cbr" onClick="setMode('cbr'); update()" checked="checked" />CBR

</div>

<div>

<input type="radio" name="mode" value="vbr" onClick="setMode('vbr'); update()" />VBR

</div>

<div>

<input type="checkbox" id="isICRDVisible" onClick="update()"/>Show init_cpb_removal_delay

</div>

<div>

<input type="checkbox" id="isICRDOVisible" onClick="update()"/>Show init_cpb_removal_delay_offset

</div>

</div>

</body>

</html>

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

151

152

153

154

155

156

157

158

159

160

161

162

163

164

165

166

167

168

169

170

171

172

173

174

175

176

177

178

179

180

181

182

183

184

185

186

187

188

// Save this as "script.js"

var canvas;

var picture = new Array();

var pictureDuration = 900900;

var initial_cpb_removal_delay = 900900;

var initial_cpb_removal_delay_offset = 90090;

var cbr_flag = true;

function init()

{

canvas = document.getElementById('canvas');

resetStream();

update();

}

function resetStream()

{

var bit_rate = document.getElementById('bitRate').value * 1000;

var averagePicSize = pictureDuration / 27000000 * bit_rate / 8;

for(var i = 0; i < 10; i++){

picture[i] = averagePicSize + (Math.random() - 0.5) * averagePicSize;

}

function tickToX(tick)

{

return tick / 900900 * 64;

}

function levelToY(level)

{

return canvas.height - level / 50;

}

function drawDecodePictures(ctx)

{

ctx.strokeStyle = 'rgba(255, 0, 0, 255)';

ctx.beginPath();

ctx.moveTo(0, levelToY(0));

ctx.lineTo(tickToX(initial_cpb_removal_delay), levelToY(0));

var prevX = tickToX(initial_cpb_removal_delay)

var prevLevel = 0;

for(var i = 0; i < 50; i++){

var level = prevLevel + picture[i];

var x1 = prevX;

var x2 = prevX + tickToX(pictureDuration)

var y = levelToY(level);

ctx.lineTo(x1, y);

ctx.lineTo(x2, y);

prevLevel = level;

prevX = x2

}

ctx.stroke();

}

function levelFromPeriod(period, bitRate)

{

return period / 27000000.0 * bitRate / 8;

}

function drawInputData(ctx)

{

var t_af = new Array();

var t_ai = new Array();

var t_ai_earliest = new Array();

var t_rn = new Array();

var bit_rate = document.getElementById('bitRate').value * 1000;

t_ai[0] = 0;

t_af[0] = picture[0] * 8 * 27000000 / bit_rate;

t_rn[0] = initial_cpb_removal_delay;

for(var n = 1; n < picture.length; n++)

{

t_rn[n] = t_rn[n - 1] + pictureDuration;

if(cbr_flag == true)

{

t_ai[n] = t_af[n - 1];

}

else

{

t_ai_earliest = t_rn[n] - (initial_cpb_removal_delay + initial_cpb_removal_delay_offset);

t_ai[n] = Math.max(t_af[n - 1], t_ai_earliest);

}

t_af[n] = t_ai[n] + picture[n] * 8 * 27000000 / bit_rate;

}

ctx.strokeStyle = 'rgba(0, 0, 255, 255)';

ctx.beginPath();

ctx.moveTo(tickToX(0), levelToY(0));

var level = 0;

for(var n = 0; n < picture.length; n++)

{

ctx.lineTo(tickToX(t_ai[n]), levelToY(level));

level += picture[n];

ctx.lineTo(tickToX(t_af[n]), levelToY(level));

}

ctx.stroke();

level = 0;

for(var n = 0; n < picture.length; n++)

{

var isICRDVisible = document.getElementById("isICRDVisible").checked;

if(isICRDVisible){

// draw initial_cpb_removal_delay period

var icrd_x1 = tickToX(t_rn[n] - initial_cpb_removal_delay)

var icrd_x2 = tickToX(t_rn[n])

var icrd_y = levelToY(level) - 4

ctx.strokeStyle = 'rgba(0, 0, 0, 255)';

ctx.beginPath();

ctx.moveTo(icrd_x1, icrd_y);

ctx.lineTo(icrd_x2, icrd_y);

ctx.stroke();

ctx.beginPath();

ctx.moveTo(icrd_x1 + 2, icrd_y - 2);

ctx.lineTo(icrd_x1, icrd_y);

ctx.lineTo(icrd_x1 + 2, icrd_y + 2);

ctx.stroke();

ctx.beginPath();

ctx.moveTo(icrd_x2 - 2, icrd_y - 2);

ctx.lineTo(icrd_x2, icrd_y);

ctx.lineTo(icrd_x2 - 2, icrd_y + 2);

ctx.stroke();

}

var isICRDOVisible = document.getElementById("isICRDOVisible").checked;

if(isICRDOVisible){

// draw initial_cpb_removal_delay period

var icrdo_x1 = tickToX(t_rn[n] - initial_cpb_removal_delay - initial_cpb_removal_delay_offset)

var icrdo_x2 = icrd_x1

var icrdo_y = levelToY(level) - 4

ctx.strokeStyle = 'rgba(0, 0, 0, 255)';

ctx.beginPath();

ctx.moveTo(icrdo_x1, icrdo_y);

ctx.lineTo(icrdo_x2, icrdo_y);

ctx.stroke();

ctx.beginPath();

ctx.moveTo(icrdo_x1 + 2, icrdo_y - 2);

ctx.lineTo(icrdo_x1, icrdo_y);

ctx.lineTo(icrdo_x1 + 2, icrdo_y + 2);

ctx.stroke();

ctx.beginPath();

ctx.moveTo(icrdo_x2 - 2, icrdo_y - 2);

ctx.lineTo(icrdo_x2, icrdo_y);

ctx.lineTo(icrdo_x2 - 2, icrdo_y + 2);

ctx.stroke();

}

level += picture[n];

}

function setMode(mode)

{

cbr_flag = mode == "cbr";

}

function updateUI(uiName, valueName)

{

document.getElementById(uiName).innerHTML = document.getElementById(valueName).value

}

function update()

{

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

ctx.fillStyle = 'rgba(255, 255, 255, 255)';

ctx.fillRect(0, 0, canvas.width, canvas.height);

updateUI("showBitRate", "bitRate");

updateUI("showICRD", "initial_cpb_removal_delay");

updateUI("showICRDO", "initial_cpb_removal_delay_offset");

initial_cpb_removal_delay = document.getElementById('initial_cpb_removal_delay').value * 27000;

initial_cpb_removal_delay_offset = document.getElementById('initial_cpb_removal_delay_offset').value * 27000;

drawDecodePictures(ctx);

drawInputData(ctx);

};

HRD Emulator in HTML5的更多相关文章

PhoneJS - HTML5 JavaScript 移动开发框架
大伙儿都知道有很多基于HTML5的移动应用框架.下一代开发工具将帮助开发者远离那些难学和让人费劲的原生SDK语言,如Objective-C,Java等.大家都知道,HTML5代表着交叉平台如移动应用程 ...
【javascript】html5中使用canvas编写头像上传截取功能
[javascript]html5中使用canvas编写头像上传截取功能本人对canvas很是喜欢,于是想仿照新浪微博头像上传功能(前端使用canvas) 本程序目前在谷歌浏览器和火狐浏览器测试可用 ...
提高HTML5 canvas性能的几种方法
简介 HTML5 canvas 最初起源于苹果(Apple)的一项实验,现在已经成为了web中受到广泛支持的2D快速模式绘图(2Dimmediate mode graphic)的标准.许多开发者现在利 ...
移动web开发前准备知识了解（html5、jquery）笔记
1.经常使用插件工具 chrome插件: Mobile & Tablet Emulator(用于常见移动端适配):(重点) Mobile Emulator is an useful o ...
使用HTML5开发Kinect体感游戏
一.简介我们要做的是怎样一款游戏? 在前不久成都TGC2016展会上,我们开发了一款<火影忍者手游>的体感游戏,主要模拟手游章节<九尾袭来 >,用户化身四代,与九尾进行对决, ...
读书笔记：《HTML5开发手册》--HTML5新的结构元素
读书笔记:<HTML5开发手册> (HTML5 Developer's CookBook) 虽然从事前端开发已有很长一段时间,对HTML5标签也有使用,但在语义化上面理解还不够清晰.之前在 ...
HTML5 Boilerplate - 让页面有个好的开始
最近看到了HTML5 Boilerplate模版,系统的学习与了解了一下.在各种CSS库.JS框架层出不穷的今天,能看到这么好的HTML模版,感觉甚爽.写篇博客,推荐给大家使用. 一:HTML5 ...
戏说HTML5
如果有非技术人员问你,HTML5是什么,你会怎么回答? 新的HTML规范... 给浏览器提供了牛逼能力,干以前不能干的事...(确切地说应该是给浏览器规定了许多新的接口标准,要求浏览器实现牛逼的功能. ...
nw.js桌面软件开发系列第0.1节 HTML5和桌面软件开发的碰撞
第0.1节 HTML5和桌面软件开发的碰撞当我们谈论桌面软件开发技术的时候,你会想到什么?如果不对技术本身进行更为深入的探讨,在我的世界里,有这么多技术概念可以被罗列出来(请原谅我本质上是一个Win ...

随机推荐

bash: cannot create temp file for here-document: Read-only file system
文件系统被强制只读问题,第一眼看到百度了一下,说可能磁盘坏了.卧槽我都吓懵了系统盘坏了,闹着玩呢,然后接着查资料,排查 mount 查看所有挂载,发现根目录的挂载权限是ro只读. /dev/sda2 ...
OPENSSL生成SSL自签证书
OPENSSL生成SSL自签证书目前,有许多重要的公网可以访问的网站系统(如网银系统)都在使用自签SSL证书,即自建PKI系统颁发的SSL证书,而不是部署支持浏览器的SSL证书. 支持浏览器的SSL ...
实现 js 数据类型的判断函数type
type = (obj) => { const pass1 = typeof obj if (pass1 != 'object') return pass1 const pass2 = obj ...
html5的audio实现高仿微信语音播放效果
效果图前台大体呈现效果图如下: 点击就可以播放mp3格式的录音.点击另外一个录音,当前录音停止! 思路关于播放动画,这个很简单,我们可以用css3的逐帧动画来实现.关于逐帧动画,我之前的文章也写过 ...
Double.parseDouble(String s)
要把字符串转换为Double类型,只能转换“0.02”这种格式的字符串,不能转换百分比格式的,比如“2%” 这个时候可以Double cbl= Double.parseDouble(“2%”.repl ...
POJ 2531-Network Saboteur(dfs)
题目链接:https://vjudge.net/problem/POJ-2531 最大流-最小割问题: https://wenku.baidu.com/view/54323c030722192e453 ...
从小白到区块链工程师：第一阶段：Go语言中的函数学习（6）
一. 为什么要有函数我们在以后的编码过程中,有很多代码会重复出现,这些重复实现的代码,我们不需要每次需要用到的时候都编写,我们将重复的代码封装起来.比如在一个网站中,无论是消费的金额还是积分的积累等 ...
Area POJ - 1265 -皮克定理-叉积
Area POJ - 1265 皮克定理是指一个计算点阵中顶点在格点上的多边形面积公式,该公式可以表示为2S=2a+b-2, 其中a表示多边形内部的点数,b表示多边形边界上的点数,S表示多边形的面积. ...
BZOJ.3227.[SDOI2008]红黑树tree(树形DP 思路)
BZOJ orz MilkyWay天天做sxt! 首先可以树形DP:\(f[i][j][0/1]\)表示\(i\)个点的子树中,黑高度为\(j\),根节点为红/黑节点的最小红节点数(最大同理). 转移 ...
prufer编码
看51nod的一场比赛,发现不会大家都A的一道题,有关prufer的我去年4月就埋下prufer这个坑,一直没解决 prufer编码是什么对于一棵无根树的生成的序列,prufer序列可以和无根树一 ...

HRD Emulator in HTML5

HRD Emulator in HTML5的更多相关文章

随机推荐

热门专题