Transcript lecture-31-33 - WordPress.com

Chapter 19: Using Media
and Streaming
Understanding the Streaming Process
• Streaming media are files that are sent in pieces by a service
and played back by a client as the delivery continues.
Streamed material can be live or on-demand.
• Live streaming is called progressive streaming or progressive
download, while on-demand streaming is from material that is
already stored to disk. In order to stream content successfully,
the system requires that the network bandwidth be adequate
to support the transfer of enough material to support user
playback. For cloud computing where the media files are large
and the connection is slow, this is a major consideration and
potential
bottleneck.
• When a live stream is sent multicast to 1,000
concurrent users at 500 kbps, the number of
megabytes transferred is calculated like this:
• MB transferred = Bandwidth x Time x Number of
Users
• MB transferred = 500 kbps x 3600 s x 1000/(8 x 1,024
x 1024)
• The amount of data transferred during streaming can
be enormous. Assuming that you have a one-hour
video file transferred at 300 kbps and encoded into a
window that is 800X600 pixels in size, on-demand
streaming would require the following:
• Size (MB) = Time (seconds) x bit rate (bps)/(mebibyte), where
a mebibyte (MiB) is 8 x 1,024 x 1,024 bits
• (3,600 x 300,000 bps)/ 8,388,608 = 128 MiB or about 135
MB/hour
• Because 1 kbps is equal to 1,000 bps, in the line above 300
kbs is equal to 300,000 bps. Notice that this calculation uses
mebibytes (MiB). A MiB is a measurement of the number of
binary bytes in units of 2^20, which is what the prefix mebiindicates.
• A MiB is equal to 2^20 or 1,048,576 bytes.
Protocol in use
• A digital audio or video file is partitioned into many small
pieces
and
played
back
at
high
speed.
Depending upon the nature of the material, playing streamed
material can suffer a certain amount of loss of transmitted
packets, which is displayed as dropped frames or missing
notes
without
the
viewer
noticing. This difference between streamed media and
transferred media is fundamental in deciding which transfer
protocol to use. For transferred media, the entire file must be
transmitted
with
fidelity,
thus TCP (Transmission Control Protocol) is the transmission
protocol. In a streamed media scenario, fidelity isn't a
prerequisite, thus UDP (User Datagram Protocol) is the
transmission
protocol.
Cloud computing advantages
•
• Access to large scale storage, which enable the storage of large media files and on-demand
media libraries.
•
Amazon S3, Microsoft Windows Azure Blob Storage, Nirvanix, EMC Atmos Online, Mezo,
Google Storage for Developers. Rackspace CloudFiles, and Eucalyptus are examples of some
of the large cloud storage systems available to content providers. Some of these systems,
such as Microsoft Azure and Google Storage, support the applications developers' position on
those SaaS services.
•
• Access to scalable compute engines and network storage that can serve as the streaming
server to large audiences.
•
• Access to a scalable compute engines that can be useful when you want to perform
encoding/decoding or transcoding on media files.
The company Encoding.com is an example of a transcoding service where you can use an
Adobe AIR application to drag and drop files that are encoded right to your desktop.
• Access to content delivery networks or edge systems that can push content out to users
based on geographical location.
Audio streaming
• Audio streaming makes much lower demands on network
bandwidth than video streaming does.
• An audio file is roughly 500 times smaller than a
correspondingly long video file. Therefore, the first streaming
services that appeared even before broadband became widely
available were audio streaming services.
• An early entrant into this area was Real Networks' Real Player
technology and its associated protocol suite. There was a time
when many content providers required you to use RealAudio
technology and the RealPlayer media player.
• Two other competing formats appeared that have gotten general
acceptance: Windows Media Player and Apple QuickTime.
These players play video formats as well as audio formats, and
all are available as stand-alone players or as browser plug-ins.
Working with VOIP applications
•
Voice over IP or VoIP is a set of communication protocols for delivering voice over
the Internet. Some of these services have been migrated to the cloud,
particularly those services that require the involvement of large number of
servers. VoIP uses additional protocols and standards other than audio
streaming; these are the most commonly used VoIP standards:
• H.323 H.323 is a recommendation from the ITU Telecommunication
Standardization Sector (ITU-T) that defines the protocols to provide audio-visual
communication sessions on any packet network.
• IP Multimedia Subsystem (IMS)
• Media Gateway Control Protocol (MGCP)
• Session Initiation Protocol (SIP)
• Real-time Transport Protocol (RTP)
• Session Description Protocol (SDP)
•
•
Skype
Google voice and Google talk
Video Streaming
• Video streaming over the Internet has become one of
the major broadcast transmission media in a rather
short time. Many trends have come together to help
make this transition a reality, including broadband
networks, high-capacity commodity disk drives, lowcost computing power, and now cloud computing.
Video streaming is one of these technologies that
benefits greatly from deployment in the cloud.
Television in cloud
• Television is a very important industry. The
average American watches five hours of TV a
day, and $70 billion a year is spent on
advertising. The number of TV watchers
dwarfs the 1 billion PC users, and
even the 2 billion cell phone users.
Worldwide, there are 4 billion TV watchers.
Streaming video formats
• • Firefox 4 (WebM)
• Chrome (h.264 supported now, WebM enabled
version available via Early Release Channel)
• Opera 10.6+ (WebM)
• Apple Safari (h.264, version 4+)
• Microsoft Internet Explorer 9 (h.264, Platform
Preview 3)
• Microsoft Internet Explorer 6, 7, or 8 with Google
Chrome Frame installed
You should expect HTML5 to be standard in the official
release versions of these browsers before 2010
ends.
• You also can view HTML 5 content in the following media players:
• Media Player Classic (http://mpc-hc.sourceforge net/)
• Moovida Core (http://www moovida.com/)
• VLC (http://www.videolan.org/)
• Winamp (http://www.winamp.com/media-player/)
• XBMC (http://xbmc.org/)
Video formats are only half of the story when it comes to video file
formats. The second half of the story is the format for the
streaming protocol that encodes the video file. Several of these
container formats are in use.
The most widely used streaming video file container format is
H.264/MPEG-4 Part 10. MPEG-4 Part 10 is also known as MPEG-4
AVC, which stands for Advanced Video Coding.
• Youtube