�ݺ�ߣ

Podcasting and Serving
Multimedia
Prepared by:
Kishan N. Patel
IT Department,
SVMIT Bharuch

Podcasting
 A podcast is a digital medium that consists of an episodic series
of audio, video, digital radio, PDF, or ePub files subscribed to
and downloaded through web syndication or streamed on-line to a computer
or mobile device
 Podcasting is the distribution of specially encoded multimedia content
(normally MP3 files with ID3 tags) to subscribed personal computers via the
RSS 2.0 protocol.
 It is a form of narrowcasting, which sends content to people who have
decided to listen, as opposed to broadcasting, which goes to everyone within a
certain radius of the signal.
2

Podcasters versus Podcatchers
 Podcasters are the people who create the content.
 Podcatchers are those who listen to the content.
3

Potcatching Clients
 The first podcatching client was iPodder, created by Adam Curry, the former
MTV VJ.
 iPodder is now called Juice Receiver and is freely downloadable.
 Juice Receiver is a so-called aggregator that accesses the podcasts to which
you have subscribed, retrieves any enclosed multimedia content, manages
files for iTunes and iPhoto, and deletes old podcasts from your hard drive
after they have expired.
4

Rss Podcast Example
 RSS templates for making podcasts are at
www.udel.edu/fth/podcasting.
 There you will find a simple example called simple.xml and a more
complex example called complete.xml.
 The simple example contains the minumum RSS for creating a podcast.
 The complete example contains optional tags used by iTunes.
5

Simple RSS Example
<?xml version="1.0"?>
<rss version="2.0">
<channel>
<title>Introduction to Podcasting</title>
<link>http://www.udel.edu/fth/podcasting/simple.xml</link>
<description>How to create a podcast</description>
<language>en-us</language>
<managingEditor>fth@udel.edu (Fred Hofstetter)</managingEditor>
<lastBuildDate>Fri, 03 Mar 2006 19:13:45 GMT</lastBuildDate>
<item>
<title>Introduction</title>
<description>What is podcasting?
</description>
<pubDate>Fri, 03 Mar 2006 01:15:00 GMT</pubDate>
<author>fth@udel.edu (Fred Hofstetter)</author>
<enclosure url="http://www.udel.edu/fth/podcasting/intro.mp3"
type="audio/x-mp3" length="114688"/>
<guid>http://www.udel.edu/fth/2006/03/03/podcasting/intro</guid>
</item>
</channel>
</rss>
6

Validating a Feed
 After you create an RSS file, you should validate the feed to make sure it does
not contain syntactical errors that may cause the podcast to fail.
 You can validate the feed for free at http://feedvalidator.org.
7

Advertising Your Feed
 If you want your feed to be listed at podcast directories and listing
sites, you can go to the site’s ping form, fill out the form, and click
Submit.
 Some ping forms are at:
 audio.weblogs.com/api.html
 www.allpodcasts.com/Update.aspx
 www.technorati.com/ping.html
8

Where to Find Podcasts
 The directory that started it all was iPodder, owned by and now called Podcast
Alley at podcastalley.com.
 You can register and create favorites at podcastpickle.com.
 Yahoo’s audio search is at audio.search.yahoo.com
 A directory of directories is at podcast411.com.
 iTunes U; watch the movie about iTunes U at www.apple.com/education/
itunesu_mobilelearning/itunesu.html
9

Podcasting from a Blog
 If you have a blog, you can use Feed Burner to turn your blog into a podcast.
This is called “burning your feed.”
 Feed Burner automatically creates and hosts the podcast’s RSS feed for you.
10

Issues in Serving Multimedia
 Even though you can serve multimedia documents on the Web as you can any
other document, multimedia causes two kinds of issues:
1. Multimedia documents can be very big and serving them requires a lot of
bandwidth.
2. Unlike text and image formats for which a small number of standardized
and interoperable formats have emerged, there are a number of different and
often proprietary multimedia formats for which interoperability is poor.
11

Cont..
 One of the motivations of these different formats is to provide compression
techniques that reduce the size of the documents and the consumption of
bandwidth.
 On the other hand, optimizing document size and bandwidth means that you
have to choose the best format depending on your constraints, and these two
issues are tightly linked.
12

Multimedia
 Difference between multimedia applications and the applications we’ve seen
so far is the notion of streaming.
 A popular multimedia application is to simulate radio or television stations on
the Net and synchronize what your users hear or see.
 This is quite different from common Internet applications where each user
reads each page at his or her own rhythm. Streaming applications require
specific techniques.
13

The Formats Labyrinth
It is categerised as follows:
1. MP3 is an audio
2. Ogg is a container format
 Descriptive formats that convey some kind of information about multimedia
streams or documents.
 Container formats that envelope multimedia streams.
 Documents and encoding formats that encode the actual audio or video.
14

Descriptive Formats
 Descriptive formats are used to describe a set of multimedia resources. They
do not include any bit of multimedia as such, but use URLs to point to
multimedia streams.
1. M3U: The simplest of all the descriptive formats is MPEG Version 3.0 URL
(M3U). M3U playlist is a plain text file with a list of URLs. Each URL is
placed on a single line and lines that start with a hash character (#) are
considered to be comments.
2. PLS: PLS playlists are formatted like Windows .ini files and their media
type is audio/x-scpls.
3. SMIL: Another approach to playlists is to use Synchronized Multimedia
Integration Language (SMIL). SMIL (pronounced smile) is a W3C
recommendation for a language that, like Atom, goes well beyond defining
playlists. SMIL is about defining interactive multimedia presentations.
15

Container and Encoding
Formats
 There is thus a need to define formats that will act as envelopes for all these
types of information. These formats are known as container formats.
 What further complicates the situation is that the different types of
information carried in a container need to be synchronized and also that it must
be streamable.
 you can’t afford to send the audio for a full movie after the full video and need
to interleave frames with the different types of information.
16

Cont..
1. WAV and AIFF
The WAVeform (WAV) and Audio Interchange File Format (AIFF) container formats
are remarkable in that they are only compatible with audio formats and that in
practice they are almost exclusively used to enclose the Pulse Code Modulation
(PCM) format also used to encode audio CDs.
2. AVI
Like WAV and AIFF, AVI (Audio Video Interleave) belongs to the ancient family
of RIFF (Resource Interchange File Format).
3. ASF
Advanced Systems Format (ASF) is a Microsoft proprietary container format
introduced to be the successor of AVI. Part of the Windows Media framework, ASF
is commonly used with the corresponding proprietary formats Windows Media Audio
(WMA) for audio and Windows Media Video (WMV) for video
4. MPEG
The MPEG standards that are pertinent to this section are MPEG-1, MPEG-2, and
MPEG-4, three generations of a multipart standard
17

Protocols
 One of the first points to consider when choosing a protocol is to decide
whether HTTP is good enough or if other protocols must be introduced.
 To answer this question, you need to differentiate between two different
usages of multimedia on the Web.
 On the one hand, you have video or audio on demand, the domain of unicast;
on the other hand, you have Web TV or Web radio, the domain of multicast
with applications that stream the same multimedia content to a number of
users.
18

Cont..
1. Multicast
 Web TV and radio is a domain where HTTP would be very inefficient: the
same content would have to be sent separately to each subscriber.
 Multicast streaming protocols differentiate the stream itself from control
information needed to assert the quality of the link between the server and
its clients.
 The main protocols used to carry the stream are Real Time Protocol (RTP).
 RTP recommends that you split audio and video into two different RTP
sessions using different TCP ports so that users can subscribe independently
to audio and video and container formats are in charge of synchronizing
audio and video.
19

Cont..
2. Unicast
 Unicast corresponds to audio and video on demand, a domain where the
choice between HTTP and a specific protocol is more open than for multicast
applications.
 Using HTTP to serve multimedia is often called HTTP streaming, pseudo-
streaming, or progressive download.
 HTTP streaming is not specific to multimedia but refers to lasting HTTP
connections expecting that the client renders the results before the end of the
exchange. This technique can be used by Ajax applications and has been
formalized as the HTTP Streaming Ajax pattern.
20

�ݺ�ߣ

Podcasting

Recommended

More Related Content

Similar to Podcasting (20)

More from Kishan Patel (9)

Podcasting