13 - multimedia

8/13/2019 13 - Multimedia

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Trng Th M Trang [email protected]


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Introduction

Streaming stored multimedia

Real-time protocols


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digital

Integration of multiple media type (text,

graphics, still and moving images, animation,

sounds, and any other medium) can be represented, stored, transmitted and

processed digitally


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Classifications of various media typeso Captured vs. synthesized media

Captured media (natural) : information captured from the realworld

Example: still image, video, audio

Synthesized media (artificial) : information synthesize bythe computer

Example: text, graphics, animation

o Discrete vs. continuous media Discrete media: spaced-based, media involve the space

dimension only Continuous media: time-based, media involves both the

space and the time dimension


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Sound Video

Image

Animation

Text Graphics

Captured

From real world

Synthesized

By computer

Discrete Discrete

Continuous Continuous


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Local vs. networkedo Local: storage and presentation of multimedia

information in standalone computers

Sample applications: DVDoNetworked: involve transmission and distribution

of multimedia information on the network

Sample applications: videoconferencing, web video

broadcasting, multimedia Email, etc.


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network audio and video (continuous media)


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Fundamental characteristics:

typically delay sensitive

o end-to-end delay

o delay jitter

loss tolerant: infrequent

losses cause minor glitches

Classes of MM applications:

1) stored streaming

2) live streaming

3) interactive, real-time

Jitter is the variability of packet delays within the

same packet stream


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Example:

o Music/video onlineo You tube

o VOA

o CNN


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1. video

recorded

2. video

sent3. video received,

played out at client

streaming: at this time, client

playing out early part of video,

while server still sending later

part of video

network

delaytime


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VCR-like functionality: client can pause,rewind, fast forward, push slider bar

timing constraint for still-to-be transmitted

data: in time for playout


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Examples: Internet radio talk show

live sporting event

Streaming (as with streamingstoredmultimedia)

playback buffer

playback can lag tens of seconds after transmission

still have timing constraint

Interactivity fast forward impossible

rewind, pause possible!


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applications: IP telephony, video conference,distributed interactive worlds


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TCP/UDP/IP: best-effort service

no guarantees on delay, loss

Todays Internet multimedia applications

use application-level techniques to mitigate

(as best possible) effects of delay, loss

But you said multimedia apps requiresQoS and level of performance to be

effective!

?? ??

?

?

? ??

?

?


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1. How should the Internet evolve to

better support multimedia?2. Transport: TCP? UDP? Other

protocol?


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Introduction


Real-time protocols


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application-levelstreaming techniquesfor making the best out

of best effort service:o client-side buffering

o use of UDP versus TCP

o multiple encodings of

multimedia

jitter removal

decompression error concealment

graphical user interfacew/ controls for interactivity

Media Player


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audio, video not streamed:

no, pipelining, long delays until playout!

audio or video stored in file

files transferred as HTTP objecto received in entirety at client

o then passed to player


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browser GETs metafile (contains information of URL, type of

encoding, etc about the audio/video file)

browser launches player, passing metafile

player contacts server

server streams audio/video to player


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Introduction


Real-time protocols

o RTSP

o RTP

o RTCP


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the protocols and their application fieldo stream description: M3U, RAM, SMIL...

describe the session and content

o stream control: RTSPremote control the session

o media transport: RTPsend data and metadata

o resource reservation (if any!): RSVP, DiffServmake sure the communication path offers appropriate guaranties

otherwise Best-Effort transmissions!


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Application protocol RFC 2326

acts as a network remote control

allows a media player to control the transmissionof a media stream for exchanging controlinformation

supports the following operations:o retrieval of a media from a servero invitation of a media server to a conference

o recording of a conference


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video

server

audio

server

media descr.

web serverclient

step 1: get description (in SDP format)

step 2: open streams with RTSP

step 3: play

step 4: teardown

C

W A V


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Major methodso SETUP: server allocates resources for a

stream and starts an RTSP sessiono PLAY: starts data tx on a streamo PAUSE: temporarily halts a streamo TEARDOWN: free resources of the stream, no

RTSP session on server any more

Additional methodso OPTIONS: get available methodso ANNOUNCE: change description of media objecto DESCRIBE: get low level descr. of media objecto RECORD: server starts recording a streamo REDIRECT: redirect client to new servero SET_PARAMETER: device or encoding control


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client

C

web

server

W

media

servers

A & V

HTTP GET

presentation description (sdp)

SETUP

PLAY

RTP audio/video

RTCP

TEARDOWN


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Transport protocol RFC 3550

RTP specifies packet structure for packets

carrying audio, video datao RTP packets encapsulated in UDP segments

RTP packet provides

opayload type identification

opacket sequence numbering

o time stamping


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Payload Type: 7 bits, providing 128 possible different types of encoding;eg PCM, MPEG2 video, etc.

Sequence Number: 16 bits; used to detect packet loss

Timestamp: 32 bytes; gives the sampling instant of the first audio/videobyte in the packet; used to remove jitter introduced by the network

Synchronization Source identifier (SSRC): 32 bits; an id for the source ofa stream; assigned randomly by the sour


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works in conjunction with RTP. Used to exchange control information (report)

between the sender and the receiver

o report statistics useful to application: # packetssent, # packets lost, interarrival jitter, etc.

feedback can be used to control performance

o sender may modify its transmissions based onfeedback


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Bi ging gio trnh Computer Networking: ATop Down Approach, 5th edition, J.F Kurose

and K.W. Ross

Bi ging EE442Multimedia Networking,Jane Dong, California State University, Los

Angeles

13 - multimedia

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