The problem we face
With the popularization of Internet, the demand of audio and video signals
transmission is increasing. After the broadcasting and TV show were put on online, (which
are tremendous huge, although we’ve got Data Compression), the waiting time for the
transmission of a video become a headache since you have to wait for 40min or longer
when your bandwidth has a limitation. This is not only time costing and hard disk room
demanding; also can not satisfy the consumers’ needs. The appearance of steaming
media, has improved this situation in a certain extent.
What is streaming media?
Streaming media technology originated in the narrowband Internet period. Due to the
needs of economic development, people eagerly need a network technology for long-
distance communication of information. Since a company called net works progressive was
first established in the United States in 1994, streaming Media began to appear on the
Internet officially. In 1995, they launched a audio receiving system called ”real audio”, and
lead the turbulent flow of streaming technology trends in the next few years. In September
1997, the company changed its name to Realnetworks, which would be involved later in
this paper. But then, Apple and Microsoft saw the excellent prospects of streaming media,
with their powerful offensive competition, Realnetworks felt the existing crisis. On the other
hand, they had promoted the rapid development of the streaming media and streaming
media to make an astonishing speed which enjoys a popular support among users.
The definitions of streaming media are various and you may confuse about them. One
statement by Wolfgang Effelsberg and Ralf Steinmetz is: Streaming media refers to media
types with time constraints and a continuous data flow, mainly video and audio
transmission. Usually, streaming media technology has three main characteristics: 1. it
enables real-time or on-demand access to audio, video, and multimedia content through
the Internet. More specifically, media is stored and published on the Web in streaming
formats can be made available for access at any time. 2. Streaming media is transmitted
by a media server application, and is processed and played back by a client player
application, as it is received. Users can start playing back streaming media as soon as
enough data has been received—without having to wait for the entire file to have arrived.
As data is transferred, it is temporarily stored in a buffer until enough data has
accumulated to be properly assembled into the next sequence of the media stream. 3. A
streamed file is received, processed, and played simultaneously and immediately, leaving
behind. An important advantage of streaming media technology is the copyright protection
it provides. No copy of the content is left on the receiving device. Therefore, the recipient
can neither alter nor redistribute the content in an unauthorized manner.
By streaming media technology, the streaming transmission can be realized, which
means the audio, video or animation are transmitted continuously and uninterruptedly.
Users do not need to download the entire files, just a few seconds delay (or several
minutes which depends how horrible your internet and computer are...), you can enjoy the
movies or music. When they are played in your computer, the rest of the files will continue
to be downloaded from the server.
In early times streaming media was mainly applied in the narrowband Internet, which
was limited by bandwidth conditions. Until1999, people can only see a small video
broadcast window on the Internet. In the second half of 2000, within the scope of the
Internet as a global warming, the broadband IP network is no longer a dream. As
streaming media technology advocates and sponsors in America, RealNetworks, Microsoft,
and Apple announced to the world that they had the latest streaming media technology
solutions in broadband at almost the same time. We can see that in a short period of time,
streaming media technology was developing rapidly.
Traditional download, progressive download and streaming
Traditional download - People are used to downloading the numerous media from the
Internet. But when you are in a narrowband world, it is very inconvenient to download a
large amount of media files. You have to wait 8 hours or more to download a movie or in
some case, the download does suddenly not work. Even you might spend a lot of time
downloading media files, only to find that when you play them, they are not what you really
wanted or expected.
Until recently, audio and video on the Web was primarily a download-and-play
technology. You had to first download an entire media file before it could play. It was like
pouring milk into a glass and then drinking it. But because media files are usually very
large and take a long time to download, the only content found on the Web was short 30-
second clips—often even shorter. Even these files could take 20 minutes or longer to
download. In other words, it took a long time to pour the milk, and then it would barely
quench your thirst…this passage is from Microsoft Windows Technologies Web Site which
clearly spelled out the shortage of traditional download.
Progressive download – it is also called pseudo-streaming. It allows playback to begin
before the file is completely downloaded and it also allows playback of content that has
been received to continue, while the remainder is still being downloaded. By progressive
download users can view the beginning of the media, as the remainder is being
downloaded, and to quit the download if the content is not what the users want.
Progressive download allows audiences to see and hear the content immediately—as it is
being downloaded—but only when the download speed can be maintained at the needed
rate. If the download slows down because of the Internet connection, causing the audio
and video playback may not always stay synchronized, playback may always stay a halt,
as the player waits for the download to catch up. Nevertheless, progressive download has
to write the media file to disk, using the memory of the receiving device.
Streaming media – unlike other form of downloadable media files, streaming media is
using a new Web transfer protocols. Streaming media files are usually encoded in several
versions, optimized for different data rates. The server can even intellectively select the
best version, based on information brought back from the client regarding the platform and
the connection speed. If the connection slows down, the streaming media can be adjusted,
depending on the media server and client player software. You can easily get benefits
using a specialized streaming media server, like efficient use of the network bandwidth,
better audio and video quality, support for large numbers of users, and content copyright
How does streaming media work?
Although the principle of streaming media seems to be complex, it is usually based on
the following steps: 1.The user selects a media file, causing a request to be sent to the
Web server. 2. The Web server relays the request to the media server. 3. The Media server
streams the media file back to the user’s computer. 4 The client decodes and plays back
the media file.
Network Protocol supporting streaming media
1 . RTP
The Real-time Transport Protocol (or RTP) is an Internet protocol standard that
specifies a way for programs to manage the real-time transmission of multimedia data over
either multicast network services. It provides end-to-end delivery services for data (such as
interactive audio and video) with real-time characteristics. RTP is commonly used in
Internet telephony application and provides the wherewithal to manage the data as it
arrives to best effect.
RTP components include: a sequence number, which is used to detect lost packets;
payload identification, which describes the specific media encoding so that it can be
changed if it has to adapt to a variation in bandwidth; frame indication, which marks the
beginning and end of each frame; source identification, which identifies the originator of the
frame; and intramedia synchronization, which uses timestamps to detect different delay
jitter within a single stream and compensate for it.
RTP combines its data transport with a control protocol (RTCP), which makes it
possible to monitor data delivery for large multicast networks. Monitoring allows the
receiver to detect if there is any packet loss and to compensate for any delay jitter. Both
protocols work independently of the underlying Transport layer and Network layer
protocols. Information in the RTP header tells the receiver how to reconstruct the data and
describes how the codec bit streams are packetized.
RTP Control Protocol (RTCP) is a sister protocol of the Real-time Transport Protocol
(RTP). It is defined in RFC 3550.
RTCP stands for Real-time Transport Control Protocol, provides out-of-band control
information for an RTP flow. It partners RTP in the delivery and packaging of multimedia
data, but does not transport any data itself. It is used periodically to transmit control
packets to participants in a streaming multimedia session. The primary function of RTCP is
to provide feedback on the quality of service being provided by RTP.
RTCP components include: quality of service (QoS) feedback, which includes the
numbers of lost packets, round-trip time, and jitter, so that the sources can adjust their data
rates accordingly; session control, which uses the RTCP BYE packet to allow participants
to indicate that they are leaving a session; identification, which includes a participant's
name, e-mail address, and telephone number for the information of other participants; and
intermedia synchronization, which enables the synchronization of separately transmitted
audio and video streams.
Real Time Streaming Protocol (RTSP) was proposed by Netscape and RealNetworks
jointly. This protocol defines how to deliver media data effectively by one-to-many
applications through IP networks. The structure of RTSP is based on RTP and RTCP. It
uses RTP or TCP to complete the data transmission. Compared with HTTP, HTTP
transmits HTML, RTSP transmits media data. The request of HTTP is sent by the client,
and the server responses; For RTSP, client and server can both send a request which
means the RTSP is a two-way protocol.
Real-Time Streaming Protocol establishes and controls one or several streaming
media of consecutive time synchronization. Despite the possibility of cross of the
continuous media streaming and control streaming, usually it does not send continuous
streaming itself. In other words, RTSP serves as the remote control of network multimedia.
RTSP does not bind with the transmission layer, such as TCP. When RTSP is in
connection, RTSP server users can open or close a number of reliable transmission
connections as to send a RTSP request. In addition, the user can use connectionless
transport protocol, such as UDP.
Some RTSP servers use RTP as the transport protocol for the actual audio/video data.
Many RTSP servers use RealNetworks's proprietary RDT as the transport protocol.
The Resource Reservation Protocol (RSVP) is a network layer protocol designed to
reserve resources across a network for an integrated services Internet. RSVP does not
transport application data but is rather an Internet control protocol, like ICMP, IGMP, or
routing protocols. RSVP provides receiver-initiated setup of resource reservations for
multicast or unicast data flows with scaling and robustness.
RSVP can be used by either hosts or routers to request or deliver specific levels of quality
of service (QoS) for application data streams or flows. RSVP defines how applications
place reservations and how they can relinquish the reserved resources once the need for
them has ended. RSVP operation will generally result in resources being reserved in each
node along a path. Because audio and video data streaming is more sensitive than
traditional data in the aspects of networks delay, the transmission of high-quality audio and
video needs much more other conditions in addition to the bandwidth requirements. RSVP
is developed by the Internet Resource Reservation Protocol. Using RSVP, part of the use
of network resources (bandwidth) can be set aside, which can provide QoS in the
transmission of streaming media in a certain extent.
RSVP is not itself a routing protocol and was designed to interoperate with current and
future routing protocols.
It is worth noting that RSVP by itself is rarely deployed in telecommunications networks
today . However, the traffic engineering extension of RSVP, or RSVP-TE,
is becoming more widely accepted nowadays in many QoS-oriented networks.
Streaming media architectures and their products
An architecture is an interdependent system comprised a variety of components that
all work together to perform certain functions. Streaming media architectures are
comprised of encoding and transmission methods, server software, and players. Currently,
the three most popular streaming media architectures are RealMedia, Windows Media,
and QuickTime. The streaming market is dominated by these three architectures.
RealNetworks is a provider of Internet media delivery software and services based in
Seattle, United States. The company has three best known creations: RealAudio, a
compressed audio format which has nearly the quality of CD sound; Real Video, a
compressed video format which transforms uninterrupted video data; RealFlash, a recently
high compression animation format, which was developed with the joint of Macromedia. It
makes Real system deliver the high-quality multimedia by various networks.
RealMedia audio streaming files can contain RealAudio and Real Video streams, and
several other formats like SMIL. RealNetworks produced the RealPlayer streaming media
software remains in the market place. After all, it has a long history of being in the
streaming media market with a large number of users. March 5, 2002. RealNetworks
released the final version of the RealOne (Gold version).
Windows Media is a multimedia framework for media creation and distribution for
Microsoft Windows. It consists of a software development kit with several application
programming interfaces and a number of prebuilt technologies. The product Windows
Media Player (WMP) is a digital media player and media library application that is used for
playing audio, video and images on personal computers running the Microsoft Windows
operating system, as well as on Pocket PC and Windows Mobile-based devices. The suffix
of files is .wmv and .asf.
The ASF (Advanced Stream Format) is the core of Windows Media. Microsoft ASF is
defined as the simultaneous media containers unified format. ASF is a data, audio, video,
images and other multimedia information format through the control of orders script and
realized the transmission of streaming media content in the form of data packets to the
network. ASF’s greatest advantage is small in size and therefore suitable for network
transmission. Using Microsoft Windows Media Player, this format can be played directly.
Users can make graphics, sound and animation into one ASF format data. Other formats of
video and audio can also be converted to in ASF format. Moreover, users can also use
sound card and video capture cards, such as a microphone to maintain data recorders so
as to save an ASF format.
In addition to being a media player, Windows Media Player includes the ability to rip
music from, and copy music to compact discs, synchronize content with a digital audio
player (MP3 player) or other mobile devices, and let users purchase or rent music from a
number of online music stores.
QuickTime is a multimedia framework developed by Apple Inc., capable of handling
various formats of digital video, media clips, sound, text, animation, music, and several
types of interactive panoramic images.
Apple QuickTime is the first video industry standards. After the release of version 4.0
of QuickTime in 1999, it began to support for real-time broadcast. Everyone is very
satisfied with QuickTime 5.0 with all aspects of functional which is simple and intuitive and
this is its greatest strength. The later version of Apple QuickTime has upgraded the quality
The suffix of files is .mov.
Unfortunately, the three parallel standards are not compatible with each other. This
means that each major network required a different device so as to translate the signal into
video and audio. That means, the RealMedia server cannot stream Windows Media and
QuickTime files; the Windows Media server cannot stream QuickTime and RealMedia files;
and the QuickTime server cannot stream RealMedia and Windows Media files. For
example, each home would have needed an ABC television set, a CBS television set, and
an NBC television set, if the household wanted to watch programs on every channel.
Each of architecture has pro and cons. Although these three architectures look similar,
in different situation you should use different one. Your project, your audience, your
objectives, and other factors are all to be considered.
Effect and influence of streaming media
With the rapid development of the information society, media streaming media
technology has played a leading role on the Internet, which includes video-on-demand;
distance education, video conference, advertising network and Internet broadcast news.
The unprecedented application has made it easy for people to get the world of information
and make emotional exchanges. It is generally optimistic about the future development of
streaming media technology. Streaming media has become the mainstream of the Internet
applications and its extensive and unique charm has captured the Internet market so as to
promote innovation and stimulate the development of the information economy. From
today's perspective, streaming media effect and influence is very positive and encouraging.
Adobe Dynamic Media Group (2001) A Streaming Media Primer
Dale Sorenson (2001) MacInTouch Special Report: Streaming Media Market
Report – 2001 http://macintouch.com/stream2001.html#companies
Real-Time Transport Protocol (2002)
Real Time Streaming Protocol http://en.wikipedia.org/wiki/RTSP
What is Streaming Media and how does it work?
Resource reservation protocol