Report on HTML& Video on Demand
Content
HTML
INTRODUCTION
HTML is the language that powers the Web in many respects, as the lingua franca that Web browsers are expected to be able to render. HTML has had unprecedented levels of success, and the uptake is all the more surprising when you realise that it was only invented in 1990, and few people knew about it before 1993.In fact, although HTML has changed relatively little since those early days, the history of HTML is rather cloudy. However, with a little detective work on the Web, it is possible to reconstruct most of the events that led to the creation and subsequent deployment and accept ion of HTML. HTML was invented for the Internet by Tim Berners-Lee at CERN, the European Laboratory for Particle Physics (CERN) in Geneva. HTML documents are created as plain-text (ASCII) files using any text editor (e.g.-Emacs or VI on UNIX machines; EDIT on a Macintosh; Notepad on a Windows machine). Tim Berners-Lee first came up with this code for his WWW project in 1990. The first mention of him working on code for processing Hypertext can be found in the original Hypertext.m file that Tim worked on; dated 25th September 90.From the 27th to the 30th November 1990, Tim and Robert Cailliau attended ECHT '90- the European Hypertext Convention. After ECHT '90, it appears that he had some more ideas about the (probably as yet unnamed) World Wide Web, and in the last few months of 1990, he started to produce more code, and also the first recorded HTML documents.
DEFINITION
Hyper Text Markup Language (HTML) is a language which runs on a computer that has a web browser installed in it. It has a collection of styles (indicated by tags) that define the various components of a World Wide Web document. HTML is a language for describing web pages where:
HTML stands for Hyper Text Markup Language HTML is not a programming language, it is a markup language A markup language is a set of markup tags HTML uses markup tags to describe web pages
On another view, Hyper Text Markup Language (HTML) is the language for specifying mainly the static content of web pages and creation of web pages and other information viewable in a browser where:
Hypertext refers to the fact that Web pages are more than just text, can contain
multimedia, and provide links for jumping within & without
Markup refers to the fact that it works by augmenting text with special symbols (tags)
that identify structure and content type
CONTENTS OF A HTML DOCUMENT
The default HTML document contains the following: HTML document is constructed using HTML tags
Certain tags are always part of a standard HTML document. Every HTML document should start with the tag <Html> and end with the tag
</Html> which tells the browser that this is an HTML document.
Each HTML document includes a head and a body. The head includes information
about the document (possibly the title, author, date of creation, software used to create the document) and the body contains the content of the document. There are tags used to identify these sections.
<Head> </Head> these tags surround the head of the document and come first (before
the body tags).
<Body> </Body> these tags surround the content of the document.
Within the title tags the document should contain a document title - this title is typically shown in the title bar of the browser window. Document titles should convey something useful about the content of the document. Sometimes for separating paragraphs we have to use a tag namely <P> which provides for a blank line. When text needs to start from a new line and not continue on the same line without skipping a blank line, then we can insert line break tag <BR>.
TYPICAL HTML DOCUMENT STRUCTURE
A typical HTML document goes like this <Html> <Head> <Title> Page Title Goes Here </Title> </Head> <Body> Content goes here </Body> </Html>
DIFFERENT HTML ELEMENTS
The HTML element tells the web browser that the file contains HTML-coded instruction. The file extension .html indicates that this is an HTML document. An HTML document must contain this extension for it to be read by a web browser. HEAD element <Head>: The Head element identifies the first part of the HTML-coded document that contains the title. The title is shown as part of browser window <Head> <Title></Title> </Head> TITLE Element <Title>: The Title element contains the document’s title and identifies its contents in a global context. The title is displayed somewhere on the browser window, but not within the text area. ADDRESS Element <Address>: Just as the title can be placed in the title bar of the browser window, certain information is commonly placed at the foot of the web page. Copyright information, contact details of the company, etc. are placed at the foot of the web page. The HTML tags used for this purpose are: <Address> </Address>
The above tag should be placed immediately after the last line of the textual material of the web page. BODY Element <Body>: The second and the largest part of any HTML document is the body which contains the contents of the document (displayed within the text area of the browser window).The tags used to indicate the start and the end of the main body of textual information are: <Body> </Body>
The default characteristics of a page such as background colour, text colour, font size, and font weight, etc. can be specified as attributes of the <Body> tag. The attributes for the <Body> tag are as follows:
1. BGCOLOUR- changes the default background colour as per the specified colour. 2. BACKGROUND- this command specifies the name of the GIF file that will be used as the background of the document.
3. TEXT- this command changes the body text colour from its default value to the
colour specified with this attribute. Example: <Html> <Head> <Title> A Simple HTML Example </Title> </Head> <Body Text = Red> Welcome to the world of HTML </Body> </Html>
SECTION HEADINGS
HTML has six levels of Section headings numbered 1 through 6, with 1 being the most prominent Section. Text with heading tags is displayed in larger and/or bolder fonts than the
normal body text by a web browser. The first heading in each document should be tagged as <H1>. The syntax of the heading element is: <Hy> Text of Heading </Hy> where y is a number between 1 and 6 specifying the level of the heading. Example: <Html> <Head> <Title> A Simple HTML Example </Title> </Head> <Body Text = Red> <H1> Welcome to the world of HTML </H1> We Love this. <H2> Start from here </H2> </Body> </Html>
LISTS
Using HTML, we can arrange items in lists in several ways. The two most commonly used methods are: a) Bulleted
b) Numbered Bulleted Lists <UL>: This is an unordered list. In this, each item (paragraph) is prefaced with a bullet. The tags used for this are <UL> and </UL>. We can also put one list with in another list simply by beginning the new list with the appropriate list tag. Example: <Html> <Head> <Title> A Simple HTML Example </Title> </Head> <Body BGCOLOUR = Red> <H3> Welcome to the world of HTML </H3> <P> <UL> <LI> Section 1 </LI> <LI> Section 2 </LI> <LI> Section 3 </LI> </UL></P> </Body> </Html>
Numbered List <OL>: Numbered list is a list with numbers in an order ascending or descending. In this, each item is prefaced with a number. The tags used for this are <OL> and </OL>. The browser applies the appropriate number to each line when it opens the page. Ordered lists have additional attributes that we can use to specify the first number of the list, as well as to create hierarchical information. Example: <Html>
<Head> <Title> A Simple HTML Example </Title> </Head> <Body BGCOLOUR = Red> <H1> Align= Left>Sample Lists</H1> <OL> <LI> Lions </LI> <LI> Tigers </LI> <LI> Bears </LI> </OL> </Body> </Html>
HYPERTEXT LINKS
When we want to link one HTML document to other HTML document, we can use hypertext links. Clicking on a section of text or an image containing such a link in one web page will open an entire web page or an image of the linked web page. The text or an image that provides such linkages is known as Hypertext or Hyperlinks or Hotspot. There are two types of links. These are: a) Links to an external document b) Links to a specific place within the same document
Link to an external document: Links are created in a web page by using <A></A> tags. Anything written between the <A> </A> tags becomes a hyperlink. Clicking on the hyperlink navigation to a different web page or image takes place. The document to be navigated need to be specified. Links are made up of three parts. These are: an anchor tag, <A> an attribute, HREF=” <A HREF=” “> “, which is located within the opening anchor tag, like </A>
an address (called a URL), which tells the browser about the file to link to. URLs identify file locations on the web or on your local hard drive. Example: <Html> <Head> <Title> A simple HTML Example </Title> </Head> <Body> <H1> HTML is very easy to learn </H1> <P> Welcome to the world of HTML </P> <A HREF=”a:\link\fig.htm”>Click here to go to next Example </A> </Body> </Html>
Link (jumps) to a specific place within the same document: Sometimes a jump is required to a different location in the same document. Since the jump has to be targeted to a specific location , therefore, first identify a location with a name and then jump to that location using the name to be used. Here the file name will be the name of the file where we are lining the text. <A HREF=”# location_name”> </A>
The absence of the filename.htm before the # symbol indicates that a jump is required within the same document.
IMAGES
HTML allows placing of static and animated images in a web page. HTML accepts picture file formats .gif and .jpg. Using tools, images can be created to suit the requirements of a web page. An image can be inserted into a web page using the tag <IMG> </IMG>. This tag takes the name of the image file as an attribute. In addition to it, HTML also allows control of the height, width, border, etc. Of every image placed on the web page. The attributes associated with the <IMG> tag are as follows:
a) ALIGN: controls alignment of the text that appears after the image. b) BORDER: specifies the size of the border to place around the image.
c) WIDTH: specifies the width of the image in pixels. d) HEIGHT: specifies the height of the image in pixels. e) HSPACE: indicates the amount of space to the left and right of the image f) VSPACE: indicates the amount of space to the top and bottom of the image
To add an image to the basic document, we have to 1) Insert an <IMG> tag where we want the image to appear. 2) Add an SRC=” “attribute pointing to the image file name.
3) The first level heading was centered to consider adding a <CENTER> tag around the logo to center it.
Example: <Html> <Head> <Title> Output</Title> </Head> <Body> <CENTER><IMG SRC=”c:\abc.gif”><BR></CENTER> We provide you with the stuff </Body> </Html>
TABLES
Tables are a flexible way to line up items according to a grid pattern. A grid pattern can be a very effective way to provide visual cohesion. Table Element: The element TABLE is used to define tables. Within the table element, we can use the TR element for table rows, TH for table headers, TD for table data, and the CAPTION element for the table’s caption. Table Attributes: There are different table attributes associated with the use of tables. These are as follows:
a) Align: The horizontal alignment of the table on-screen (not the contents of the
table).Possible values are as follows-
bleedleft- aligned at the left window border bleedright- aligned at the right window border center- centered between text margins justify- table should fill space between text margins left- at the left text margin right- at the right text margin
b) Border- Causes browser to render a border around the table; if missing, the table has
no grid around it or its data.
c) Cellpadding: Can be used to set the number of pixels between cells of the table. d) Cellspacing: Can be used to set the number of pixels around the data in the cells. e) Caption Element: This element is used to label a figure or table. Its attribute is Align,
which is used to position the caption relative to the figure or table.
f) The TH & TD Element: The TH element identifies a table header cell, and TD
identifies a table data cell. Browsers usually treat these two elements differently in terms of how they are rendered.
g) The TR Element: The TR element identifies a container for a row of table cells. Its
attributes are the same as that for TH and TD. Example: <Html> <Head> <Title>Table Sample</Title> </Head> <Body> <TABLE Border=”2” Cellpadding=”3” Cellspacing=”3”> <CAPTION>The Extreme Cup Results</CAPTION> <TR><TH>Game</TH><TH>Red Wings</TH><TH>Black Hawks</TH></TR>
<TR><TD Align=”center”>1</TD Align=”center”> <TD Align=”center”>3</TD Align=”center”> <TD Align=”center”>2</TD Align=”center”></TR> <TR><TD Align=”center”>2</TD Align=”center”> <TD Align=”center”>4</TD Align=”center”> <TD Align=”center”>1</TD Align=”center”> </TR> <TR><TD Align=”center”>3</TD Align=”center”> <TD Align=”center”>0</TD Align=”center”> <TD Align=”center”>8</TD Align=”center”> </TR> <TR><TD Align=”center”>4</TD Align=”center”> <TD Align=”center”>8</TD Align=”center”> <TD Align=”center”>7</TD Align=”center”> </TR> </TABLE> </Body> </Html>
VIDEO ON
DEMAND
INTRODUCTION
Video on demand systems allow users to select and watch/listen to video or audio content on demand and is sometimes compared to an electronic video rental store. The user selects any one of a large number of available videos and takes it home to view. Only with video on demand, the selection is made at home using the TV’s remote control and the video starts immediately. If video on demand is going to compete successfully with video rental stores, it may be necessary to allow users to stop, start and rewind videos at will. Giving users this ability virtually forces the video provider to transmit separate copy to each one. The existing DTH services being provided by various companies like Dish TV, Tata Sky, Big TV and others are using the concept of video on demand in their packages. VoD systems either stream content through a set-top box, allowing viewing in real time, or download it to a device such as a computer, digital video recorder, personal video recorder or portable media player for viewing at any time. The majority of cable- and telcobased television providers offer both VOD streaming, such as pay-per-view, whereby a user
buys or selects a movie or television program and it begins to play on the television set almost instantaneously, or downloading to a DVR rented from the provider, for viewing in the future.
OVERVIEW OF A VIDEO ON DEMAND SYSTEM
The general model that describes a video on demand system is as shown below. Here, we see a high bandwidth wide area backbone network at the center of the system. Connected to it are thousands of local distribution networks such as Cable TV or telephone company distribution systems. The local distribution systems reach into people’s houses, where they terminate in set-top boxes, which are, in fact, powerful, specialized personal computers.
Attached to the backbone by high bandwidth optical fibers are numerous information providers. Some of these will offer pay per view. Also included in the system are local spooling servers that allow videos to be placed closer to the users, to save bandwidth during peak hours. To have video on demand, we need video servers capable of storing and outputting a large number of movies simultaneously. When compressed in MPEG-2, a normal movie occupies roughly 4GB of storage. Since a video server is really just a massive real time I/O device, it needs a different hardware and software architecture than a PC or UNIX workstations. It typically includes servers. The server has one or more highperformance CPUs, each with some local memory, a shared main memory, a massive RAM cache for popular movies, a variety of storage devices for holding the movies and some networking hardware, normally an optical interface to a SONET or ATM backbone at OC-12 or higher. The CPUs are used for accepting user requests, locating movies, moving data between devices, customer billing and many other functions. The heart of the video server software is the disk management software.
PROBLEMS IN VOD
A video-on-demand system typically is characterized by the flexibility it offers to its
subscribers. A true video-on-demand service should provide its remote subscribers total control over the presentation session. It should incorporate all the functionalities of a local media play such as fast-forwarding, rewinding and randomized frame access with very little response time and near-broadcast quality. Some common problems/issues a Video-on-Demand needs to address are:
1.
Load distribution on server : To support multiple connection requests from user,
and facilitate minimum response time.
2.
Media content management : This includes high storage space, effective content
management, replication strategy etc.
3.
Adapt to dynamic network bandwidth : As the client-server link may not
always be consistent, one needs to manage the content corresponding to network change and still maintain quality of the media.
4.
Decide on Buffer/Cache: To facilitate user with better quality and high-response time,
the system may have to decide upon the buffer size and cache.
5.
Rate control : For adapting to network, the system may need to vary the transport
and encoding rates.
6.
Scalability and cost effectiveness. To provide reliability and availability
7.
In addition to these parameters, such a set-up needs to be highly fault-tolerant and fairly scalable to ensure subscriber satisfaction. Several architectures are proposed in this regard which address the above mentioned issues by employing expensive hardware infrastructure.
INTRODUCTION
HTML is the language that powers the Web in many respects, as the lingua franca that Web browsers are expected to be able to render. HTML has had unprecedented levels of success, and the uptake is all the more surprising when you realise that it was only invented in 1990, and few people knew about it before 1993.In fact, although HTML has changed relatively little since those early days, the history of HTML is rather cloudy. However, with a little detective work on the Web, it is possible to reconstruct most of the events that led to the creation and subsequent deployment and accept ion of HTML. HTML was invented for the Internet by Tim Berners-Lee at CERN, the European Laboratory for Particle Physics (CERN) in Geneva. HTML documents are created as plain-text (ASCII) files using any text editor (e.g.-Emacs or VI on UNIX machines; EDIT on a Macintosh; Notepad on a Windows machine). Tim Berners-Lee first came up with this code for his WWW project in 1990. The first mention of him working on code for processing Hypertext can be found in the original Hypertext.m file that Tim worked on; dated 25th September 90.From the 27th to the 30th November 1990, Tim and Robert Cailliau attended ECHT '90- the European Hypertext Convention. After ECHT '90, it appears that he had some more ideas about the (probably as yet unnamed) World Wide Web, and in the last few months of 1990, he started to produce more code, and also the first recorded HTML documents.
DEFINITION
Hyper Text Markup Language (HTML) is a language which runs on a computer that has a web browser installed in it. It has a collection of styles (indicated by tags) that define the various components of a World Wide Web document. HTML is a language for describing web pages where:
HTML stands for Hyper Text Markup Language HTML is not a programming language, it is a markup language A markup language is a set of markup tags HTML uses markup tags to describe web pages
On another view, Hyper Text Markup Language (HTML) is the language for specifying mainly the static content of web pages and creation of web pages and other information viewable in a browser where:
Hypertext refers to the fact that Web pages are more than just text, can contain
multimedia, and provide links for jumping within & without
Markup refers to the fact that it works by augmenting text with special symbols (tags)
that identify structure and content type
CONTENTS OF A HTML DOCUMENT
The default HTML document contains the following: HTML document is constructed using HTML tags
Certain tags are always part of a standard HTML document. Every HTML document should start with the tag <Html> and end with the tag
</Html> which tells the browser that this is an HTML document.
Each HTML document includes a head and a body. The head includes information
about the document (possibly the title, author, date of creation, software used to create the document) and the body contains the content of the document. There are tags used to identify these sections.
<Head> </Head> these tags surround the head of the document and come first (before
the body tags).
<Body> </Body> these tags surround the content of the document.
Within the title tags the document should contain a document title - this title is typically shown in the title bar of the browser window. Document titles should convey something useful about the content of the document. Sometimes for separating paragraphs we have to use a tag namely <P> which provides for a blank line. When text needs to start from a new line and not continue on the same line without skipping a blank line, then we can insert line break tag <BR>.
TYPICAL HTML DOCUMENT STRUCTURE
A typical HTML document goes like this <Html> <Head> <Title> Page Title Goes Here </Title> </Head> <Body> Content goes here </Body> </Html>
DIFFERENT HTML ELEMENTS
The HTML element tells the web browser that the file contains HTML-coded instruction. The file extension .html indicates that this is an HTML document. An HTML document must contain this extension for it to be read by a web browser. HEAD element <Head>: The Head element identifies the first part of the HTML-coded document that contains the title. The title is shown as part of browser window <Head> <Title></Title> </Head> TITLE Element <Title>: The Title element contains the document’s title and identifies its contents in a global context. The title is displayed somewhere on the browser window, but not within the text area. ADDRESS Element <Address>: Just as the title can be placed in the title bar of the browser window, certain information is commonly placed at the foot of the web page. Copyright information, contact details of the company, etc. are placed at the foot of the web page. The HTML tags used for this purpose are: <Address> </Address>
The above tag should be placed immediately after the last line of the textual material of the web page. BODY Element <Body>: The second and the largest part of any HTML document is the body which contains the contents of the document (displayed within the text area of the browser window).The tags used to indicate the start and the end of the main body of textual information are: <Body> </Body>
The default characteristics of a page such as background colour, text colour, font size, and font weight, etc. can be specified as attributes of the <Body> tag. The attributes for the <Body> tag are as follows:
1. BGCOLOUR- changes the default background colour as per the specified colour. 2. BACKGROUND- this command specifies the name of the GIF file that will be used as the background of the document.
3. TEXT- this command changes the body text colour from its default value to the
colour specified with this attribute. Example: <Html> <Head> <Title> A Simple HTML Example </Title> </Head> <Body Text = Red> Welcome to the world of HTML </Body> </Html>
SECTION HEADINGS
HTML has six levels of Section headings numbered 1 through 6, with 1 being the most prominent Section. Text with heading tags is displayed in larger and/or bolder fonts than the
normal body text by a web browser. The first heading in each document should be tagged as <H1>. The syntax of the heading element is: <Hy> Text of Heading </Hy> where y is a number between 1 and 6 specifying the level of the heading. Example: <Html> <Head> <Title> A Simple HTML Example </Title> </Head> <Body Text = Red> <H1> Welcome to the world of HTML </H1> We Love this. <H2> Start from here </H2> </Body> </Html>
LISTS
Using HTML, we can arrange items in lists in several ways. The two most commonly used methods are: a) Bulleted
b) Numbered Bulleted Lists <UL>: This is an unordered list. In this, each item (paragraph) is prefaced with a bullet. The tags used for this are <UL> and </UL>. We can also put one list with in another list simply by beginning the new list with the appropriate list tag. Example: <Html> <Head> <Title> A Simple HTML Example </Title> </Head> <Body BGCOLOUR = Red> <H3> Welcome to the world of HTML </H3> <P> <UL> <LI> Section 1 </LI> <LI> Section 2 </LI> <LI> Section 3 </LI> </UL></P> </Body> </Html>
Numbered List <OL>: Numbered list is a list with numbers in an order ascending or descending. In this, each item is prefaced with a number. The tags used for this are <OL> and </OL>. The browser applies the appropriate number to each line when it opens the page. Ordered lists have additional attributes that we can use to specify the first number of the list, as well as to create hierarchical information. Example: <Html>
<Head> <Title> A Simple HTML Example </Title> </Head> <Body BGCOLOUR = Red> <H1> Align= Left>Sample Lists</H1> <OL> <LI> Lions </LI> <LI> Tigers </LI> <LI> Bears </LI> </OL> </Body> </Html>
HYPERTEXT LINKS
When we want to link one HTML document to other HTML document, we can use hypertext links. Clicking on a section of text or an image containing such a link in one web page will open an entire web page or an image of the linked web page. The text or an image that provides such linkages is known as Hypertext or Hyperlinks or Hotspot. There are two types of links. These are: a) Links to an external document b) Links to a specific place within the same document
Link to an external document: Links are created in a web page by using <A></A> tags. Anything written between the <A> </A> tags becomes a hyperlink. Clicking on the hyperlink navigation to a different web page or image takes place. The document to be navigated need to be specified. Links are made up of three parts. These are: an anchor tag, <A> an attribute, HREF=” <A HREF=” “> “, which is located within the opening anchor tag, like </A>
an address (called a URL), which tells the browser about the file to link to. URLs identify file locations on the web or on your local hard drive. Example: <Html> <Head> <Title> A simple HTML Example </Title> </Head> <Body> <H1> HTML is very easy to learn </H1> <P> Welcome to the world of HTML </P> <A HREF=”a:\link\fig.htm”>Click here to go to next Example </A> </Body> </Html>
Link (jumps) to a specific place within the same document: Sometimes a jump is required to a different location in the same document. Since the jump has to be targeted to a specific location , therefore, first identify a location with a name and then jump to that location using the name to be used. Here the file name will be the name of the file where we are lining the text. <A HREF=”# location_name”> </A>
The absence of the filename.htm before the # symbol indicates that a jump is required within the same document.
IMAGES
HTML allows placing of static and animated images in a web page. HTML accepts picture file formats .gif and .jpg. Using tools, images can be created to suit the requirements of a web page. An image can be inserted into a web page using the tag <IMG> </IMG>. This tag takes the name of the image file as an attribute. In addition to it, HTML also allows control of the height, width, border, etc. Of every image placed on the web page. The attributes associated with the <IMG> tag are as follows:
a) ALIGN: controls alignment of the text that appears after the image. b) BORDER: specifies the size of the border to place around the image.
c) WIDTH: specifies the width of the image in pixels. d) HEIGHT: specifies the height of the image in pixels. e) HSPACE: indicates the amount of space to the left and right of the image f) VSPACE: indicates the amount of space to the top and bottom of the image
To add an image to the basic document, we have to 1) Insert an <IMG> tag where we want the image to appear. 2) Add an SRC=” “attribute pointing to the image file name.
3) The first level heading was centered to consider adding a <CENTER> tag around the logo to center it.
Example: <Html> <Head> <Title> Output</Title> </Head> <Body> <CENTER><IMG SRC=”c:\abc.gif”><BR></CENTER> We provide you with the stuff </Body> </Html>
TABLES
Tables are a flexible way to line up items according to a grid pattern. A grid pattern can be a very effective way to provide visual cohesion. Table Element: The element TABLE is used to define tables. Within the table element, we can use the TR element for table rows, TH for table headers, TD for table data, and the CAPTION element for the table’s caption. Table Attributes: There are different table attributes associated with the use of tables. These are as follows:
a) Align: The horizontal alignment of the table on-screen (not the contents of the
table).Possible values are as follows-
bleedleft- aligned at the left window border bleedright- aligned at the right window border center- centered between text margins justify- table should fill space between text margins left- at the left text margin right- at the right text margin
b) Border- Causes browser to render a border around the table; if missing, the table has
no grid around it or its data.
c) Cellpadding: Can be used to set the number of pixels between cells of the table. d) Cellspacing: Can be used to set the number of pixels around the data in the cells. e) Caption Element: This element is used to label a figure or table. Its attribute is Align,
which is used to position the caption relative to the figure or table.
f) The TH & TD Element: The TH element identifies a table header cell, and TD
identifies a table data cell. Browsers usually treat these two elements differently in terms of how they are rendered.
g) The TR Element: The TR element identifies a container for a row of table cells. Its
attributes are the same as that for TH and TD. Example: <Html> <Head> <Title>Table Sample</Title> </Head> <Body> <TABLE Border=”2” Cellpadding=”3” Cellspacing=”3”> <CAPTION>The Extreme Cup Results</CAPTION> <TR><TH>Game</TH><TH>Red Wings</TH><TH>Black Hawks</TH></TR>
<TR><TD Align=”center”>1</TD Align=”center”> <TD Align=”center”>3</TD Align=”center”> <TD Align=”center”>2</TD Align=”center”></TR> <TR><TD Align=”center”>2</TD Align=”center”> <TD Align=”center”>4</TD Align=”center”> <TD Align=”center”>1</TD Align=”center”> </TR> <TR><TD Align=”center”>3</TD Align=”center”> <TD Align=”center”>0</TD Align=”center”> <TD Align=”center”>8</TD Align=”center”> </TR> <TR><TD Align=”center”>4</TD Align=”center”> <TD Align=”center”>8</TD Align=”center”> <TD Align=”center”>7</TD Align=”center”> </TR> </TABLE> </Body> </Html>
VIDEO ON
DEMAND
INTRODUCTION
Video on demand systems allow users to select and watch/listen to video or audio content on demand and is sometimes compared to an electronic video rental store. The user selects any one of a large number of available videos and takes it home to view. Only with video on demand, the selection is made at home using the TV’s remote control and the video starts immediately. If video on demand is going to compete successfully with video rental stores, it may be necessary to allow users to stop, start and rewind videos at will. Giving users this ability virtually forces the video provider to transmit separate copy to each one. The existing DTH services being provided by various companies like Dish TV, Tata Sky, Big TV and others are using the concept of video on demand in their packages. VoD systems either stream content through a set-top box, allowing viewing in real time, or download it to a device such as a computer, digital video recorder, personal video recorder or portable media player for viewing at any time. The majority of cable- and telcobased television providers offer both VOD streaming, such as pay-per-view, whereby a user
buys or selects a movie or television program and it begins to play on the television set almost instantaneously, or downloading to a DVR rented from the provider, for viewing in the future.
OVERVIEW OF A VIDEO ON DEMAND SYSTEM
The general model that describes a video on demand system is as shown below. Here, we see a high bandwidth wide area backbone network at the center of the system. Connected to it are thousands of local distribution networks such as Cable TV or telephone company distribution systems. The local distribution systems reach into people’s houses, where they terminate in set-top boxes, which are, in fact, powerful, specialized personal computers.
Attached to the backbone by high bandwidth optical fibers are numerous information providers. Some of these will offer pay per view. Also included in the system are local spooling servers that allow videos to be placed closer to the users, to save bandwidth during peak hours. To have video on demand, we need video servers capable of storing and outputting a large number of movies simultaneously. When compressed in MPEG-2, a normal movie occupies roughly 4GB of storage. Since a video server is really just a massive real time I/O device, it needs a different hardware and software architecture than a PC or UNIX workstations. It typically includes servers. The server has one or more highperformance CPUs, each with some local memory, a shared main memory, a massive RAM cache for popular movies, a variety of storage devices for holding the movies and some networking hardware, normally an optical interface to a SONET or ATM backbone at OC-12 or higher. The CPUs are used for accepting user requests, locating movies, moving data between devices, customer billing and many other functions. The heart of the video server software is the disk management software.
PROBLEMS IN VOD
A video-on-demand system typically is characterized by the flexibility it offers to its
subscribers. A true video-on-demand service should provide its remote subscribers total control over the presentation session. It should incorporate all the functionalities of a local media play such as fast-forwarding, rewinding and randomized frame access with very little response time and near-broadcast quality. Some common problems/issues a Video-on-Demand needs to address are:
1.
Load distribution on server : To support multiple connection requests from user,
and facilitate minimum response time.
2.
Media content management : This includes high storage space, effective content
management, replication strategy etc.
3.
Adapt to dynamic network bandwidth : As the client-server link may not
always be consistent, one needs to manage the content corresponding to network change and still maintain quality of the media.
4.
Decide on Buffer/Cache: To facilitate user with better quality and high-response time,
the system may have to decide upon the buffer size and cache.
5.
Rate control : For adapting to network, the system may need to vary the transport
and encoding rates.
6.
Scalability and cost effectiveness. To provide reliability and availability
7.
In addition to these parameters, such a set-up needs to be highly fault-tolerant and fairly scalable to ensure subscriber satisfaction. Several architectures are proposed in this regard which address the above mentioned issues by employing expensive hardware infrastructure.
