The web Programming: 2014

Friday, 2 May 2014

HTML Videos

Videos can be embedded in HTML pages with several methods.

Playing Videos in HTML

Example

Try it yourself »

Problems, Problems, and Solutions

Playing videos in HTML is not easy!
You must add a lot of tricks to make sure your video will play in all browsers (Internet Explorer, Chrome, Firefox, Safari, Opera) and on all hardware (PC, Mac , iPad, iPhone).
In this chapter W3Schools summarizes the problems and the solutions.

HTML Video - Using <embed>

The <embed> tag defines a container for external (non-HTML) content.
The following HTML fragment displays a Flash video embedded in a web page:

Example

Try it yourself »

Problems

If the browser does not support Flash, the video will not play
iPad and iPhone do not support Flash videos

HTML Video - Using <object>

The <object> tag tag can also define a container for external (non-HTML) content.
The following HTML fragment displays a Flash video embedded in a web page:

Example

Try it yourself »

Problems:

If the browser does not support Flash, the video will not play
iPad and iPhone do not support Flash videos

The HTML5 <video> Element

The HTML5 <video> tag defines a video or movie.
The <video> element works in all modern browsers.
The following example uses the HTML5 <video> tag, which specifies one MP4 file (for Internet Explorer, Chrome, Firefox 21+, and Safari), and one OGG file (for older Firefox and Opera). If something fails, it will display a text:

Example

<video width="320" height="240" controls>
<source src="movie.mp4" type="video/mp4">
<source src="movie.ogg" type="video/ogg">
Your browser does not support the video tag.
</video>

Try it yourself »

Problems:

You must convert your videos to many different formats
The <video> element does not work in older browsers

HTML Video - The Best Solution

The best solution is to use the HTML5 <video> element + the <embed> element.
The example below uses the <video> element and tries to play the video either as MP4 or OGG. If that fails, the code "falls back" to try the <embed> element:

HTML 5 + <object> + <embed>

Try it yourself »

Problems:

You must convert your videos to many different formats

HTML Video - YouTube Solution

However, maybe the easiest way to display videos in HTML pages, is to use YouTube (see next chapter)!

HTML Video - Using A Hyperlink

If a web page includes a hyperlink to a media file, most browsers will use a "helper application" to play the file.
The following code fragment displays a link to a Flash video. If a user clicks on the link, the browser will launch a helper application to play the file:

Example

<a href="intro.swf">Play a video file</a>

Try it yourself »

Tips About Inline Videos

When a video is included in a web page it is called inline video.
If you plan to use inline videos, be aware that many people find it annoying. Also note that some users might have turned off the inline video option in their browser.
Our best advice is to include inline videos only in pages where the user expects to see a video. An example of this is a page which opens after the user has clicked on a link to see the video.

HTML Multimedia Tags

= Tag added in HTML5.

Tag	Description
<embed>	Defines an embedded object
<object>	Defines an embedded object
<param>	Defines a parameter for an object
<audio>	Defines sound content
<video>	Defines a video or movie
<source>	Defines multiple media resources for media elements (<video> and <audio>)
<track>	Defines text tracks for media elements (<video> and <audio>)

HTML Sounds / Audio

Sounds can be embedded in HTML pages with several methods.

Problems, Problems, and Solutions

Playing audio in HTML is not easy!
You must know a lot of tricks to make sure your audio files will play in all browsers (Internet Explorer, Chrome, Firefox, Safari, Opera) and on all hardware (PC, Mac , iPad, iPhone).
In this chapter W3Schools summarizes the problems and the solutions.

Using Plug-ins

A plug-in is a small computer program that extends the standard functionality of the browser.
Plug-ins can be added to HTML pages using the <object> tag or the <embed> tag.
These tags define containers for resources (normally non-HTML resources), which, depending on the type, will either be displayed by the browsers, or by an external plug-in.

HTML Audio - Using <embed>

The <embed> tag defines a container for external (non-HTML) content.
The following code fragment should play an MP3 file embedded in a web page:

Example

Try it yourself »

Problems:

Different browsers support different audio formats
If a browser does not support the file format, the audio will not play without a plug-in
If the plug-in is not installed on the users' computer, the audio will not play

HTML Audio - Using <object>

The <object> tag can also define a container for external (non-HTML) content.
The following code fragment should play an MP3 file embedded in a web page:

Example

Try it yourself »

Problems:

Different browsers support different audio formats
If a browser does not support the file format, the audio will not play without a plug-in
If the plug-in is not installed on the users' computer, the audio will not play

The HTML5 <audio> Element

The HTML5 <audio> tag defines sound, such as music or other audio streams.
The <audio> element works in all modern browsers.
The following example uses the HTML5 <audio> tag, which specifies one MP3 file (for Internet Explorer, Chrome, Firefox 21+, and Safari), and one OGG file (for older Firefox and Opera). If something fails, it will display a text:

Example

<audio controls>
<source src="horse.mp3" type="audio/mpeg">
<source src="horse.ogg" type="audio/ogg">
Your browser does not support this audio format.
</audio>

Try it yourself »

Problems:

You must convert the audio files into different formats
The <audio> element does not work in older browsers

HTML Audio - The Best Solution

The best solution is to use the HTML5 <audio> element + the <embed> element.
The example below uses the <audio> element and tries to play the audio either as MP3 or OGG. If that fails, the code "falls back" to try the <embed> element:

Example

Try it yourself »

Problems:

You must convert the audio files into different formats
The <embed> element cannot "fall-back" to display an error message

HTML Audio - Using A Hyperlink

If a web page includes a hyperlink to a media file, most browsers will use a "helper application" to play the file.
The following code fragment displays a link to an MP3 file. If a user clicks on the link, the browser will launch a helper application to play the file:

Example

<a href="horse.mp3">Play the sound</a>

Try it yourself »

Tips About Inline Sounds

When sound is included in a web page, or as part of a web page, it is called inline sound.
If you plan to use inline sounds, be aware that many people will find it annoying. Also note that some users might have turned off the inline sound option in their browser.
Our best advice is to include inline sounds only in pages where the user expects to hear sounds. An example of this is a page which opens after the user has clicked on a link to hear a recording.

HTML Multimedia Tags

= Tag added in HTML5.

Tag	Description
<embed>	Defines an embedded object
<object>	Defines an embedded object
<param>	Defines a parameter for an object
<audio>	Defines sound content
<video>	Defines a video or movie
<source>	Defines multiple media resources for media elements (<video> and <audio>)
<track>	Defines text tracks for media elements (<video> and <audio>)

HTML - Plug-ins

The purpose of a plug-in, is to extend the functionality of the HTML browser.

HTML Helpers (Plug-ins)

A helper application is a small computer program that extends the standard functionality of the browser. Helper applications are also called plug-ins.
Examples of well-known plug-ins are Java applets and Adobe Flash Player.
Plug-ins can be added to web pages with the <object> tag or the <embed> tag.
Plug-ins can be used for many purposes: to display maps, scan for viruses, verify your bank id, and much more. The restrictions are few.

What is The Best Way to Play Audio or Video in HTML?

The best way to embed audio in a web page is to use the HTML5 <audio> element.
The best way to embed video in a web page is to use the HTML5 <video> element.

The <object> Element

The <object> element is supported in all major browsers.
The <object> element defines an embedded object within an HTML document.
It is used to to embed plug-ins (like Java applets, ActiveX, PDF, and Flash) in web pages.
It can also be used to embed another webpage, or web content like images, into HTML documents.

	The text between <object> and </object> is displayed if the browser doesn't support the tag. The HTML <param> tag is used to pass parameters to the plug in.

Example

Try it yourself »

The <embed> Element

The <embed> element is supported in all major browsers.
The <embed> element defines a container for an external application or interactive content (a plug-in).
Many web browsers have supported the <embed> element for a long time. However, it has not been a part of the HTML specification before HTML5.
The <embed> element will validate in an HTML5 page, but not in an HTML 4 page.

Example

Try it yourself »

	Note that the <embed> element does not have a closing tag. It can not contain alternative text.

HTML Multimedia

Multimedia on the web is sound, music, videos, movies, and animations.

What is Multimedia?

Multimedia comes in many different formats. It can be almost anything you can hear or see.
Examples: Pictures, music, sound, videos, records, films, animations, and more.
Modern web pages often have embedded multimedia elements, and modern browsers have support for various multimedia formats.
In this tutorial you will learn about the different multimedia formats.

Internet Browser Support

The first Internet browsers had support for text only, and even the text support was limited to a single font in a single color. Then came browsers with support for colors, fonts and text styles, and support for pictures was also added.
The support for sounds, animations, and videos is handled in different ways by various browsers. Some multimedia elements is supported, and some requires an extra helper program (a plug-in) to work.
You will learn more about plug-ins in the next chapters.

Multimedia Formats

Multimedia elements (like sounds or videos) are stored in media files.
The most common way to discover the type of a file, is to look at the file extension. When a browser sees the file extension .htm or .html, it will treat the file as an HTML file. The .xml extension indicates an XML file, and the .css extension indicates a style sheet file. Pictures are recognized by extensions like .gif, .png and .jpg.
Multimedia files also have their own formats and different extensions like: .swf, .wav, .mp3, .mp4, .mpg, .wmv, and .avi.

Video Formats

MP4 is the new and upcoming format for internet video.

MP4 is recommended by YouTube.

MP4 is supported by Flash players and HTML5.

Format	File	Description
AVI	.avi	AVI (Audio Video Interleave) was developed by Microsoft, and is therefore playable on all Windows computers. It is commonly used in video cameras and TV hardware, but is difficult to play on non-Windows computers.
WMV	.wmv	WMV (Windows Media Video) was developed by Microsoft, and is therefore playable on all Windows computers. It is commonly used in video cameras and by TV hardware, but is difficult to play on non-Windows computers.
QuickTime	.mov	QuickTime was developed by Apple, and is therefore playable on all Apple computers. It is commonly used in video cameras and by TV hardware, but is difficult to play on non-Apple computers.
RealVideo	.rm .ram	RealVideo was developed by Real Media to allow video streaming with low bandwidths. It is still used for online video and Internet TV, but because of the low bandwidth priority, the quality is also low.
Flash	.swf .flv	Flash was developed by Macromedia. Flash requires an extra component to play in a browser.
Ogg	.ogg	Theora Ogg was developed by the Xiph.Org Foundation.
WebM	.webm	WebM is a project (www.webmproject.org) by the web giants, Mozilla, Opera, Adobe, and Google.
MPEG	.mpg .mpeg	MPEG, developed by the Moving Pictures Expert Group, used to be the most popular video format on the Internet. It used to be supported by all major browsers, but it is not supported by HTML5.
MPEG-4 or MP4	.mp4	MP4 is the upcoming format on the internet. It is supported by all major browsers in HTML5. YouTube recommends using MP4, and it is commonly used in newer video cameras and TV hardware.

	Only MP4, WebM, and Ogg video is supported by the newest HTML5 standard.

Sound Formats

MP3 is the newest format for compressed recorded music. The term MP3 has become synonymous with digital music.
If your website is about recorded music, MP3 is the choice.

Format	File	Description
MIDI	.mid .midi	MIDI (Musical Instrument Digital Interface) is a format for electronic music devices like synthesizers and PC sound cards. MIDI files do not contain sound, but digital musical instructions (notes) that can be played by electronics (like your PC's sound card). Click here to play The Beatles. Since MIDI files only contains instructions; they are extremely small. The example above is only 23K in size, but it plays for nearly 5 minutes. MIDI is supported by many software systems/platforms. Because it is the main format for binary music, it is supported by most software, including Internet browsers.
RealAudio	.rm .ram	RealAudio was developed Real Media to allow streaming of audio (online music, Internet radio) with low bandwidths.
WMA	.wma	WMA (Windows Media Audio), compares in quality to MP3, and is compatible with most music players, except the iPod. WMA files can be delivered as a continuous flow of data, which makes it practical for use in Internet radio or on-line music.
AAC	.aac	AAC (Advanced Audio Coding) was developed by Apple as the default format for iTunes.
WAV	.wav	WAVE (more known as WAV) was developed by IBM and Microsoft. WAV is compatible with Windows, Macintosh, and Linux operating systems.
Ogg	.ogg	Ogg was developed by the Xiph.Org Foundation.
MP3	.mp3	MP3 files are actually the sound part of MPEG files. MP3 is the most popular format for music players. The encoding system combines good compression (small files) with high quality. It is supported by all major browsers.
MP4	.mp4	MP4 is a video format, but it can also be used with audio only. MP4 video is the upcoming video format on the internet. This can lead to an automatic support for MP4 audio by all major browsers.

	Only MP3, WAV, and Ogg audio is supported by the newest HTML5 standard.

HTML5 Server-Sent Events

HTML5 Server-Sent Events allow a web page to get updates from a server.

Server-Sent Events - One Way Messaging

A server-sent event is when a web page automatically gets updates from a server.
This was also possible before, but the web page would have to ask if any updates were available. With server-sent events, the updates come automatically.
Examples: Facebook/Twitter updates, stock price updates, news feeds, sport results, etc.

Browser Support

Server-Sent Events are supported in all major browsers, except Internet Explorer.

Receive Server-Sent Event Notifications

The EventSource object is used to receive server-sent event notifications:

Example

var source = new EventSource("demo_sse.php");
source.onmessage = function(event) {
document.getElementById("result").innerHTML + =event.data + "<br>";
};

Try it yourself »

Example explained:

Create a new EventSource object, and specify the URL of the page sending the updates (in this example "demo_sse.php")
Each time an update is received, the onmessage event occurs
When an onmessage event occurs, put the received data into the element with id="result"

Check Server-Sent Events Support

In the tryit example above there were some extra lines of code to check browser support for server-sent events:

if(typeof(EventSource) !== "undefined")
{
// Yes! Server-sent events support!
// Some code.....
}
else
{
// Sorry! No server-sent events support..
}

Server-Side Code Example

For the example above to work, you need a server capable of sending data updates (like PHP or ASP).
The server-side event stream syntax is simple. Set the "Content-Type" header to "text/event-stream". Now you can start sending event streams.
Code in PHP (demo_sse.php):

<?php
header('Content-Type: text/event-stream');
header('Cache-Control: no-cache');

$time = date('r');
echo "data: The server time is: {$time}\n\n";
flush();
?>

Code in ASP (VB) (demo_sse.asp):

<%
Response.ContentType = "text/event-stream"
Response.Expires = -1
Response.Write("data: " & now())
Response.Flush()
%>

Code explained:

Set the "Content-Type" header to "text/event-stream"
Specify that the page should not cache
Output the data to send (Always start with "data: ")
Flush the output data back to the web page

The EventSource Object

In the examples above we used the onmessage event to get messages. But other events are also available:

Events	Description
onopen	When a connection to the server is opened
onmessage	When a message is received
onerror	When an error occurs

HTML5 Web Workers

A web worker is a JavaScript running in the background, without affecting the performance of the page.

What is a Web Worker?

When executing scripts in an HTML page, the page becomes unresponsive until the script is finished.
A web worker is a JavaScript that runs in the background, independently of other scripts, without affecting the performance of the page. You can continue to do whatever you want: clicking, selecting things, etc., while the web worker runs in the background.

Browser Support

Internet Explorer 10, Firefox, Chrome, Safari and Opera support Web workers.

HTML5 Web Workers Example

The example below creates a simple web worker that count numbers in the background:

Example

Count numbers:

Try it yourself »

Check Web Worker Support

Before creating a web worker, check whether the user's browser supports it:

if(typeof(Worker) !== "undefined")
{
// Yes! Web worker support!
// Some code.....
}
else
{
// Sorry! No Web Worker support..
}

Create a Web Worker File

Now, let's create our web worker in an external JavaScript.
Here, we create a script that counts. The script is stored in the "demo_workers.js" file:

var i = 0;

function timedCount()
{
i = i + 1;
postMessage(i);
setTimeout("timedCount()",500);
}

timedCount();

The important part of the code above is the postMessage() method - which is used to post a message back to the HTML page.
Note: Normally web workers are not used for such simple scripts, but for more CPU intensive tasks.

Create a Web Worker Object

Now that we have the web worker file, we need to call it from an HTML page.
The following lines checks if the worker already exists, if not - it creates a new web worker object and runs the code in "demo_workers.js":

if(typeof(w) == "undefined")
{
w = new Worker("demo_workers.js");
}

Then we can send and receive messages from the web worker.
Add an "onmessage" event listener to the web worker.

w.onmessage = function(event){
document.getElementById("result").innerHTML = event.data;
};

When the web worker posts a message, the code within the event listener is executed. The data from the web worker is stored in event.data.

Terminate a Web Worker

When a web worker object is created, it will continue to listen for messages (even after the external script is finished) until it is terminated.
To terminate a web worker, and free browser/computer resources, use the terminate() method:

w.terminate();

Full Web Worker Example Code

We have already seen the Worker code in the .js file. Below is the code for the HTML page:

Example

<!DOCTYPE html>
<html>
<body>

<p>Count numbers: <output id="result"></output></p>
<button onclick="startWorker()">Start Worker</button>
<button onclick="stopWorker()">Stop Worker</button>
<br><br>

<script>
var w;

function startWorker()
{
if(typeof(Worker) !== "undefined")
{
if(typeof(w) == "undefined")
    {
    w = new Worker("demo_workers.js");
    }
w.onmessage = function (event){
    document.getElementById("result").innerHTML = event.data;
};
}
else
{
document.getElementById("result").innerHTML="Sorry, your browser does not support Web Workers...";
}
}

function stopWorker()
{
w.terminate();
}
</script>

</body>
</html>

Try it yourself »

Web Workers and the DOM

Since web workers are in external files, they do not have access to the following JavaScript objects:

The window object
The document object
The parent object

HTML5 Application Cache

With HTML5 it is easy to make an offline version of a web application, by creating a cache manifest file.

What is Application Cache?

HTML5 introduces application cache, which means that a web application is cached, and accessible without an internet connection.
Application cache gives an application three advantages:

Offline browsing - users can use the application when they're offline
Speed - cached resources load faster
Reduced server load - the browser will only download updated/changed resources from the server

Browser Support

Internet Explorer 10, Firefox, Chrome, Safari and Opera support Application cache.

HTML5 Cache Manifest Example

The example below shows an HTML document with a cache manifest (for offline browsing):

Example

<!DOCTYPE HTML>
<html manifest="demo.appcache">

<body>
The content of the document......
</body>

</html>

Try it yourself »

Cache Manifest Basics

To enable application cache, include the manifest attribute in the document's <html> tag:

<!DOCTYPE HTML>
<html manifest="demo.appcache">
...
</html>

Every page with the manifest attribute specified will be cached when the user visits it. If the manifest attribute is not specified, the page will not be cached (unless the page is specified directly in the manifest file).
The recommended file extension for manifest files is: ".appcache"

	A manifest file needs to be served with the correct MIME-type, which is "text/cache-manifest". Must be configured on the web server.

The Manifest File

The manifest file is a simple text file, which tells the browser what to cache (and what to never cache).
The manifest file has three sections:

CACHE MANIFEST - Files listed under this header will be cached after they are downloaded for the first time
NETWORK - Files listed under this header require a connection to the server, and will never be cached
FALLBACK - Files listed under this header specifies fallback pages if a page is inaccessible

CACHE MANIFEST

The first line, CACHE MANIFEST, is required:

CACHE MANIFEST
/theme.css
/logo.gif
/main.js

The manifest file above lists three resources: a CSS file, a GIF image, and a JavaScript file. When the manifest file is loaded, the browser will download the three files from the root directory of the web site. Then, whenever the user is not connected to the internet, the resources will still be available.

NETWORK

The NETWORK section below specifies that the file "login.asp" should never be cached, and will not be available offline:

NETWORK:
login.asp

An asterisk can be used to indicate that all other resources/files require an internet connection:

NETWORK:
*

FALLBACK

The FALLBACK section below specifies that "offline.html" will be served in place of all files in the /html/ catalog, in case an internet connection cannot be established:

FALLBACK:
/html/ /offline.html

Note: The first URI is the resource, the second is the fallback.

Updating the Cache

Once an application is cached, it remains cached until one of the following happens:

The user clears the browser's cache
The manifest file is modified (see tip below)
The application cache is programmatically updated

Example - Complete Cache Manifest File

CACHE MANIFEST
# 2012-02-21 v1.0.0
/theme.css
/logo.gif
/main.js

NETWORK:
login.asp

FALLBACK:
/html/ /offline.html

	Tip: Lines starting with a "#" are comment lines, but can also serve another purpose. An application's cache is only updated when its manifest file changes. If you edit an image or change a JavaScript function, those changes will not be re-cached. Updating the date and version in a comment line is one way to make the browser re-cache your files.

Notes on Application Cache

Be careful with what you cache.
Once a file is cached, the browser will continue to show the cached version, even if you change the file on the server. To ensure the browser updates the cache, you need to change the manifest file.
Note: Browsers may have different size limits for cached data (some browsers have a 5MB limit per site).

HTML5 Web Storage

HTML5 web storage, better than cookies.

What is HTML5 Web Storage?

With HTML5, web pages can store data locally within the user's browser.
Earlier, this was done with cookies. However, Web Storage is more secure and faster. The data is not included with every server request, but used ONLY when asked for. It is also possible to store large amounts of data, without affecting the website's performance.
The data is stored in name/value pairs, and a web page can only access data stored by itself.
Unlike cookies, the storage limit is far larger (at least 5MB) and information is never transferred to the server.

Browser Support

Web storage is supported in Internet Explorer 8+, Firefox, Opera, Chrome, and Safari.
Note: Internet Explorer 7 and earlier versions, do not support Web Storage.

HTML5 Web Storage Objects

HTML5 Web Storage provides two new objects for storing data on the client:

window.localStorage - stores data with no expiration date
code.sessionStorage - stores data for one session (data is lost when the tab is closed)

Before using web storage, check browser support for localStorage and sessionStorage:

if(typeof(Storage)!=="undefined")
{
// Code for localStorage/sessionStorage.
}
else
{
// Sorry! No Web Storage support..
}

The localStorage Object

The localStorage object stores the data with no expiration date. The data will not be deleted when the browser is closed, and will be available the next day, week, or year.

Example

// Store
localStorage.setItem("lastname", "Smith");
// Retrieve
document.getElementById("result").innerHTML=localStorage.getItem("lastname");

Try it yourself »

Example explained:

Create a localStorage name/value pair with name="lastname" and value="Smith"
Retrieve the value of "lastname" and insert it into the element with id="result"

The example above could also be written like this:

// Store
localStorage.lastname = "Smith";
// Retrieve
document.getElementById("result").innerHTML=localStorage.lastname;

The syntax for removing the "lastname" localStorage item is as follows:

localStorage.removeItem("lastname");

Note: Name/value pairs are always stored as strings. Remember to convert them to another format when needed!
The following example counts the number of times a user has clicked a button. In this code the value string is converted to a number to be able to increase the counter:

Example

if (localStorage.clickcount)
{
localStorage.clickcount = Number(localStorage.clickcount) + 1;
}
else
{
localStorage.clickcount = 1;
}
document.getElementById("result").innerHTML="You have clicked the button " +
localStorage.clickcount + " time(s).";

Try it yourself »

The sessionStorage Object

The sessionStorage object is equal to the localStorage object, except that it stores the data for only one session. The data is deleted when the user closes the browser window.
The following example counts the number of times a user has clicked a button, in the current session:

Example

if (sessionStorage.clickcount)
{
sessionStorage.clickcount = Number(sessionStorage.clickcount) + 1;
}
else
{
sessionStorage.clickcount = 1;
}
document.getElementById("result").innerHTML="You have clicked the button " +
sessionStorage.clickcount + " time(s) in this session.";

Try it yourself »

HTML5 Drag and Drop

Drag and drop is a part of the HTML5 standard.

Drag the W3Schools image into the rectangle.

Drag and Drop

Drag and drop is a very common feature. It is when you "grab" an object and drag it to a different location.
In HTML5, drag and drop is part of the standard, and any element can be draggable.

Browser Support

Internet Explorer 9+, Firefox, Opera, Chrome, and Safari support drag and drop.
Note: Drag and drop does not work in Safari 5.1.2.

HTML5 Drag and Drop Example

The example below is a simple drag and drop example:

Example

<!DOCTYPE HTML>
<html>
<head>
<script>
function allowDrop(ev)
{
ev.preventDefault();
}

function drag(ev)
{
ev.dataTransfer.setData("Text",ev.target.id);
}

function drop(ev)
{
ev.preventDefault();
var data = ev.dataTransfer.getData("Text");
ev.target.appendChild(document.getElementById(data));
}
</script>
</head>
<body>

<div id="div1" ondrop="drop(event)" ondragover="allowDrop(event)"></div>

<img id="drag1" src="img_logo.gif" draggable="true"
ondragstart="drag(event)" width="336" height="69"

</body>
</html>

Try it yourself »

It might seem complicated, but lets go through all the different parts of a drag and drop event.

Make an Element Draggable

First of all: To make an element draggable, set the draggable attribute to true:

What to Drag - ondragstart and setData()

Then, specify what should happen when the element is dragged.
In the example above, the ondragstart attribute calls a function, drag(event), that specifies what data to be dragged.
The dataTransfer.setData() method sets the data type and the value of the dragged data:

function drag(ev)
{
ev.dataTransfer.setData("Text",ev.target.id);
}

In this case, the data type is "Text" and the value is the id of the draggable element ("drag1").

Where to Drop - ondragover

The ondragover event specifies where the dragged data can be dropped.
By default, data/elements cannot be dropped in other elements. To allow a drop, we must prevent the default handling of the element.
This is done by calling the event.preventDefault() method for the ondragover event:

event.preventDefault()

Do the Drop - ondrop

When the dragged data is dropped, a drop event occurs.
In the example above, the ondrop attribute calls a function, drop(event):

function drop(ev)
{
ev.preventDefault();
var data = ev.dataTransfer.getData("Text");
ev.target.appendChild(document.getElementById(data));
}

Code explained:

Call preventDefault() to prevent the browser default handling of the data (default is open as link on drop)
Get the dragged data with the dataTransfer.getData("Text") method. This method will return any data that was set to the same type in the setData() method
The dragged data is the id of the dragged element ("drag1")
Append the dragged element into the drop element

More Examples

Drag image back and forth
How to drag (and drop) an image back and forth between two <div> elements.

HTML5 Geolocation

HTML5 Geolocation is used to locate a user's position

Locate the User's Position

The HTML5 Geolocation API is used to get the geographical position of a user.
Since this can compromise user privacy, the position is not available unless the user approves it.

Browser Support

Internet Explorer 9+, Firefox, Chrome, Safari and Opera support Geolocation.
Note: Geolocation is much more accurate for devices with GPS, like iPhone.

HTML5 - Using Geolocation

Use the getCurrentPosition() method to get the user's position.
The example below is a simple Geolocation example returning the latitude and longitude of the user's position:

Example

Try it yourself »

Example explained:

Check if Geolocation is supported
If supported, run the getCurrentPosition() method. If not, display a message to the user
If the getCurrentPosition() method is successful, it returns a coordinates object to the function specified in the parameter ( showPosition )
The showPosition() function gets the displays the Latitude and Longitude

The example above is a very basic Geolocation script, with no error handling.

Handling Errors and Rejections

The second parameter of the getCurrentPosition() method is used to handle errors. It specifies a function to run if it fails to get the user's location:

Example

function showError(error)
{
switch(error.code)
    {
    case error.PERMISSION_DENIED:
      x.innerHTML = "User denied the request for Geolocation."
      break;
    case error.POSITION_UNAVAILABLE:
      x.innerHTML = "Location information is unavailable."
      break;
    case error.TIMEOUT:
      x.innerHTML = "The request to get user location timed out."
      break;
    case error.UNKNOWN_ERROR:
      x.innerHTML = "An unknown error occurred."
      break;
    }
}

Try it yourself »

Error Codes:

Permission denied - The user did not allow Geolocation
Position unavailable - It is not possible to get the current location
Timeout - The operation timed out

Displaying the Result in a Map

To display the result in a map, you need access to a map service that can use latitude and longitude, like Google Maps:

Example

function showPosition(position)
{
var latlon = position.coords.latitude + "," + position.coords.longitude;

var img_url = "http://maps.googleapis.com/maps/api/staticmap?center="
+latlon+"&zoom=14&size=400x300&sensor=false";

document.getElementById("mapholder").innerHTML = "<img src='"+img_url+"'>";
}

Try it yourself »

In the example above we use the returned latitude and longitude data to show the location in a Google map (using a static image).
Google Map Script
How to use a script to show an interactive map with a marker, zoom and drag options.

Location-specific Information

This page demonstrated how to show a user's position on a map. However, Geolocation is also very useful for location-specific information.
Examples:

Up-to-date local information
Showing Points-of-interest near the user
Turn-by-turn navigation (GPS)

The getCurrentPosition() Method - Return Data

The getCurrentPosition() method returns an object if it is successful. The latitude, longitude and accuracy properties are always returned. The other properties below are returned if available.

Property	Description
coords.latitude	The latitude as a decimal number
coords.longitude	The longitude as a decimal number
coords.accuracy	The accuracy of position
coords.altitude	The altitude in meters above the mean sea level
coords.altitudeAccuracy	The altitude accuracy of position
coords.heading	The heading as degrees clockwise from North
coords.speed	The speed in meters per second
timestamp	The date/time of the response

Geolocation object - Other interesting Methods

watchPosition() - Returns the current position of the user and continues to return updated position as the user moves (like the GPS in a car).
clearWatch() - Stops the watchPosition() method.
The example below shows the watchPosition() method. You need an accurate GPS device to test this (like iPhone):

Example

Try it yourself »

HTML5 Audio

HTML5 provides a standard for playing audio files.

Audio on the Web

Before HTML5, there was no standard for playing audio files on a web page.
Before HTML5, audio files had to be played with a plug-in (like flash). However, different browsers supported different plug-ins.
HTML5 defines a new element which specifies a standard way to embed an audio file on a web page: the <audio> element.

Browser Support

Internet Explorer 9+, Firefox, Opera, Chrome, and Safari support the <audio> element.
Note: Internet Explorer 8 and earlier versions, do not support the <audio> element.

HTML5 Audio - How It Works

To play an audio file in HTML5, this is all you need:

Example

<audio controls>
<source src="horse.ogg" type="audio/ogg">
<source src="horse.mp3" type="audio/mpeg">
Your browser does not support the audio element.
</audio>

Try it yourself »

The control attribute adds audio controls, like play, pause, and volume.
You should also insert text content between the <audio> and </audio> tags for browsers that do not support the <audio> element.
The <audio> element allows multiple <source> elements. <source> elements can link to different audio files. The browser will use the first recognized format.

Audio Formats and Browser Support

Currently, there are 3 supported file formats for the <audio> element: MP3, Wav, and Ogg:

Browser	MP3	Wav	Ogg
Internet Explorer	YES	NO	NO
Chrome	YES	YES	YES
Firefox	NO Update: Firefox 21 running on Windows 7, Windows 8, Windows Vista, and Android now supports MP3	YES	YES
Safari	YES	YES	NO
Opera	NO	YES	YES

MIME Types for Audio Formats

Format	MIME-type
MP3	audio/mpeg
Ogg	audio/ogg
Wav	audio/wav

HTML5 Audio Tags

Tag	Description
<audio>	Defines sound content
<source>	Defines multiple media resources for media elements, such as <video> and <audio>

HTML5 Video

Many modern websites show videos. HTML5 provides a standard for showing them.

Check if your browser supports HTML5 video

Video on the Web

Before HTML5, there was no standard for showing videos/movies on web pages.
Before HTML5, videos could only be played with a plug-in (like flash). However, different browsers supported different plug-ins.
HTML5 defines a new element which specifies a standard way to embed a video or movie on a web page: the <video> element.

Browser Support

Internet Explorer 9+, Firefox, Opera, Chrome, and Safari support the <video> element.
Note: Internet Explorer 8 and earlier versions, do not support the <video> element.

HTML5 Video - How It Works

To show a video in HTML5, this is all you need:

Example

<video width="320" height="240" controls>
<source src="movie.mp4" type="video/mp4">
<source src="movie.ogg" type="video/ogg">
Your browser does not support the video tag.
</video>

Try it yourself »

The control attribute adds video controls, like play, pause, and volume.
It is also a good idea to always include width and height attributes. If height and width are set, the space required for the video is reserved when the page is loaded. However, without these attributes, the browser does not know the size of the video, and cannot reserve the appropriate space to it. The effect will be that the page layout will change during loading (while the video loads).
You should also insert text content between the <video> and </video> tags for browsers that do not support the <video> element.
The <video> element allows multiple <source> elements. <source> elements can link to different video files. The browser will use the first recognized format.

Video Formats and Browser Support

Currently, there are 3 supported video formats for the <video> element: MP4, WebM, and Ogg:

Browser	MP4	WebM	Ogg
Internet Explorer	YES	NO	NO
Chrome	YES	YES	YES
Firefox	NO Update: Firefox 21 running on Windows 7, Windows 8, Windows Vista, and Android now supports MP4	YES	YES
Safari	YES	NO	NO
Opera	NO	YES	YES

MP4 = MPEG 4 files with H264 video codec and AAC audio codec
WebM = WebM files with VP8 video codec and Vorbis audio codec
Ogg = Ogg files with Theora video codec and Vorbis audio codec

MIME Types for Video Formats

Format	MIME-type
MP4	video/mp4
WebM	video/webm
Ogg	video/ogg

HTML5 <video> - DOM Methods and Properties

HTML5 has DOM methods, properties, and events for the <video> and <audio> elements.
These methods, properties, and events allow you to manipulate <video> and <audio> elements using JavaScript.
There are methods for playing, pausing, and loading, for example and there are properties (like duration and volume). There are also DOM events that can notify you when the <video> element begins to play, is paused, is ended, etc.
The example below illustrate, in a simple way, how to address a <video> element, read and set properties, and call methods.

Example 1

Create simple play/pause + resize controls for a video:

Video courtesy of Big Buck Bunny.

The example above calls two methods: play() and pause(). It also uses two properties: paused and width.
Try it yourself »

For a full reference go to our HTML5 Audio/Video DOM Reference.

HTML5 Video Tags

Tag	Description
<video>	Defines a video or movie
<source>	Defines multiple media resources for media elements, such as <video> and <audio>
<track>	Defines text tracks in media players

HTML5 Inline SVG

What is SVG?

SVG stands for Scalable Vector Graphics
SVG is used to define vector-based graphics for the Web
SVG defines the graphics in XML format
SVG graphics do NOT lose any quality if they are zoomed or resized
Every element and every attribute in SVG files can be animated
SVG is a W3C recommendation

SVG Advantages

Advantages of using SVG over other image formats (like JPEG and GIF) are:

SVG images can be created and edited with any text editor
SVG images can be searched, indexed, scripted, and compressed
SVG images are scalable
SVG images can be printed with high quality at any resolution
SVG images are zoomable (and the image can be zoomed without degradation)

Browser Support

Internet Explorer 9+, Firefox, Opera, Chrome, and Safari support inline SVG.

Embed SVG Directly Into HTML Pages

In HTML5, you can embed SVG elements directly into your HTML page:

Example

<!DOCTYPE html>
<html>
<body>

<svg width="300" height="200">
<polygon points="100,10 40,180 190,60 10,60 160,180"
style="fill:lime;stroke:purple;stroke-width:5;fill-rule:evenodd;" />
</svg>

</body>
</html>

Try it yourself »

Result:
To learn more about SVG, please read our SVG Tutorial.

Differences Between SVG and Canvas

SVG is a language for describing 2D graphics in XML.
Canvas draws 2D graphics, on the fly (with a JavaScript).
SVG is XML based, which means that every element is available within the SVG DOM. You can attach JavaScript event handlers for an element.
In SVG, each drawn shape is remembered as an object. If attributes of an SVG object are changed, the browser can automatically re-render the shape.
Canvas is rendered pixel by pixel. In canvas, once the graphic is drawn, it is forgotten by the browser. If its position should be changed, the entire scene needs to be redrawn, including any objects that might have been covered by the graphic.

Comparison of Canvas and SVG

The table below shows some important differences between Canvas and SVG:

Canvas	SVG
Resolution dependent No support for event handlers Poor text rendering capabilities You can save the resulting image as .png or .jpg Well suited for graphic-intensive games	Resolution independent Support for event handlers Best suited for applications with large rendering areas (Google Maps) Slow rendering if complex (anything that uses the DOM a lot will be slow) Not suited for game applications

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Friday, 2 May 2014

Playing Videos in HTML

Example

Problems, Problems, and Solutions

HTML Video - Using <embed>

Example

HTML Video - Using <object>

Example

The HTML5 <video> Element

Example

HTML Video - The Best Solution

HTML 5 + <object> + <embed>

HTML Video - YouTube Solution

HTML Video - Using A Hyperlink

Example

Tips About Inline Videos

HTML Multimedia Tags

Problems, Problems, and Solutions

Using Plug-ins

HTML Audio - Using <embed>

Example

Problems:

HTML Audio - Using <object>

Example

Problems:

The HTML5 <audio> Element

Example

Problems:

HTML Audio - The Best Solution

Example

Problems:

HTML Audio - Using A Hyperlink

Example

Tips About Inline Sounds

HTML Multimedia Tags

HTML Helpers (Plug-ins)

What is The Best Way to Play Audio or Video in HTML?

The <object> Element

Example

The <embed> Element

Example

What is Multimedia?

Internet Browser Support

Multimedia Formats

Video Formats

Sound Formats

Server-Sent Events - One Way Messaging

Browser Support

Receive Server-Sent Event Notifications

Example

Check Server-Sent Events Support

Server-Side Code Example

The EventSource Object

What is a Web Worker?

Browser Support

HTML5 Web Workers Example

Example

Check Web Worker Support

Create a Web Worker File

Create a Web Worker Object

Terminate a Web Worker

Full Web Worker Example Code

Example

Web Workers and the DOM

What is Application Cache?

Browser Support

HTML5 Cache Manifest Example

Example

Cache Manifest Basics

The Manifest File

CACHE MANIFEST

NETWORK

FALLBACK

Updating the Cache

Example - Complete Cache Manifest File

Notes on Application Cache