HRD Emulator in HTML5

Last Update:2017-02-12 Source: Internet

Author: User

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Posted on March, from Moto

Just like MPEG-2 video uses VBV (video Buffer Verifier), H. Uses HRD (hypothetical Reference Decoder) to Defin e Correctness of streams.

One of the verification provided by HRD is CPB buffer fullness. The idea was simple; Feed H. 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 is explained here.

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

HRD Emulator (CBR)

The Blue Line is the number of bits entered to HRD over time. The input rate was constant in CBR mode, i.e. the Blue line is straight. The red line was 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 have some periods where the input rate is zero. H. 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 a. It means the first picture was decoded Ms after the first bit of the "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 blu E line).

H. Introduced another parameter to allow the reduction of initial decoding delay at the expense of Increas Ed 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. HRD provides these parameters to encoders so, they can choose optimal bit stream configuration for each target D Evices.

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

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<TITLE>HRD emulator</title>

#plot {

Float:left

}

#control-container {

Float:left

}

#widget {

Float:right;

Width:10em

}

#heading {

Float:left

}

</style>

</div>

<input id= "bitrate" onchange= "update ()" type= "range" min= "0" max= "$" value= "/>"

</div>

<div class= "Heading" >initial_cpb_removal_delay [<span id= "SHOWICRD" > </span> ms]</div>

<div>

<input id= "Initial_cpb_removal_delay" onchange= "Update ()" type= "range" min= "0" max= "+" value= "/>"

</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>

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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 < 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 < 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

This article is an English version of an article which is originally in the Chinese language on aliyun.com and is provided for information purposes only. This website makes no representation or warranty of any kind, either expressed or implied, as to the accuracy, completeness ownership or reliability of the article or any translations thereof. If you have any concerns or complaints relating to the article, please send an email, providing a detailed description of the concern or complaint, to info-contact@alibabacloud.com. A staff member will contact you within 5 working days. Once verified, infringing content will be removed immediately.

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