Transcript streaming - sharif university of technology

Video and Audio Over The Net
Mahdi Zandakbari
Vesal Hajiabbas
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Audio/Video Transition over the Net
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Streaming
–
–
–
–
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Webcasts
Online video/audio chanels
Video Conference
Audio Conference
VOIP (Voice Over IP)
Video Over IP
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Key Definitions:
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CODEC
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Encoding
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Formed from two roots compression and de-compression
CO + DEC = CODEC
Actually algorithms which are required by both the media
server and player
Refers to the process of preparing video for streaming
Streaming media
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A combination of audio and video that can be delivered to
the viewer across the internet
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Video/Audio Streaming
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First found in 1995 and soon supported by RealAudio
It enables undisrupted web broadcasts
You do not need to download the whole video/audio file
If the streaming audio/video is broadcast live, then it may
be called "realtime audio/video"
How?
– The client side stores a few seconds of the stream in a buffer
before it starts sending it to the speakers
– fast forward impossible
– rewind, pause possible!
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MM Networking Applications
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Typically delay sensitive
– end-to-end delay
– delay jitter
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But loss tolerant: infrequent losses cause
minor glitches
– Video loss is more welcome than the audio
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Streaming a videoconference
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Streaming a videoconference
makes it possible for any number
of people to view a conference –
either live or recorded for ondemand access.
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Streaming Systems Architecture
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So here are what you actually need:
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Encoder
– resource used at time of capture
– It could be software-based or hardware-based
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Server
– Platform from which the stream is dispersed to the
user
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Player
– A decoder located on the end users computer + A
player (e.g. Windows Media Player, QuickTime,
RealPlayer,…)
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Codec and format
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Codec Type
H.261
H.263
Mpeg1
Mpeg2
Mpeg3(mp3)
Mpeg4
Real Audio codecs
Microsoft formats
Expense in Real-time
(moderate)
(moderate)
(high)
(high)
Target Bandwidth
(wide rang)
(wide rang)
(1-1.5 mb)
(4-15 mb)
(high)
(high)
(high)
(less than 64kb)
(wide range)
(wide range)
Notes:
1. real-time codecs are usually expensive
2.New technologies offer dynamic coding and decoding (e.g. java
multimedia API, Mpeg-4 Syntactic description language MSIL,…)
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Streaming media standards
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All Usually based on UDP (User Datagram Protocol)
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RTSP (Real Time Streaming Protocol)
RTP (Real Time Transport Protocol)
RTCP (Real Time Control Protocol)
MSIL
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The TCP/IP protocol can not do the best here.
XML-based markup language geared toward long-form
multimedia
Packet format for Internet audio/video (streaming and
conferencing)
Datatypes and codecs
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MP3, GIF, JPEG, PNG, H.261, H.263, MPEG-4
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RTSP Operation
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Protocols map
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Commercial Real Time Video
Streamers
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MacroMedia's Streaming
Shockwave
– serverless product which relies
on the HTTP protocol only
– No live feeds
– Uses flash files (see
WWW.CNN.COM)
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Progressive Network's
RealVideo
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– VDP based
– MPEG-1 ,2 ,H.263 ,GSM
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Xing Technology's StreamWorks
– Mpeg1
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VDONet's VDOLive
– UDP based
– Uses Wavelets for compression
VXtreme
– uses a layered compression
scheme to divide the compressed
video into multiple streams
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Vivoactive
– Uses both HTTP and UDP
– H.263 video compression and
G.723 audio compression
– RSTP on UDP
– Needs RealServer 4.0
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Vosaic
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Microsoft's NetShow
– ASF files are created using
MPEG-layer3, Microsoft MPEG-4,
Vivo G.723 (audio) and H.263
(video)
– It also supports other standard
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Types of
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Multicast
– Webcast (e.g.
www.cnn.co
m)
– Could be realtime or not
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Unicast
– Video
conference
– Usually realtime
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VOIP (Voice Over IP)
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Specially refers to a
technology that enables a
voice conversation using the
Internet. (putting voice in IP
packets.
First appeared in 1995 and hit
the market depending on the
expense reductions it
introduced.
VOIP types
– PC 2 PC
– PC 2 Phone
– Phone 2 Phone
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VOIP Protocols And Standards
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Similar to streaming protocols
H.323 is the most popular in all IP based
multimedia.
Like streaming it really depends on the network
architecture
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Video Over IP
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Recently appeared due to respond to emerging
video phones
Similar to VOIP
Few additional protocols and standards
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