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Video Transmission System. Heejune AHN Embedded Communications Laboratory Seoul National Univ. of Technology Fall 200 8 Last updated 2008. 11. 23. Agenda. QoS Requirement and Constraints Impacts on Video Coding Representative Video Transmission Systems MPEG-2 PS & TS System

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Video transmission system

Video Transmission System

Heejune AHN

Embedded Communications Laboratory

Seoul National Univ. of Technology

Fall 2008

Last updated 2008. 11. 23


Agenda

Agenda

  • QoS Requirement and Constraints

  • Impacts on Video Coding

  • Representative Video Transmission Systems

    • MPEG-2 PS & TS System

    • Internet-based Video Transmission System


1 transmission video coding

1. Transmission & Video coding

  • Transmission constraints

    • Impact on the video coding system: cross-layer concepts

    • e.g. rate-control, un-equal FEC, scalable coding etc

  • QoS & QoE

    • QoS (Quality of Service)

      • network layer performance measures

      • Bit-rate (mean, variation), delay (mean, jitter), loss (bit, packet)

    • QoE (Quality of Experience)

      • Application (user) layer performance measures

network/storage

Bit-rate

Input

Video

Input

Video

decoder

encoder

Delay

Loss


Qos data rate

QoS: Data rate

  • Offered

    • Circuit Switched (constant)

      • 384kbps (WCDMA)

      • DMB, DTV

    • Packet-switched (variable)

      • Internet

      • LAN

      • ADSL connected to Internet

  • Required

    • Mean Rate

      • Required Quality

      • TV (2~5Mbps)

    • Rate-Variation

      • Scene complexity (inherent)

      • Coding scheme


Qos error distortion

QoS: Error (distortion)

  • Offered

    • Circuit switched

      • low random bit error

      • very seldom burst errors

    • Wired Packet-switched

      • almost no bit error

      • low packet loss

      • some burst packet loss

        • Due to network Congestion

    • Wireless packet-switched

      • Some bit loss

      • Some packet loss

      • Some burst packet loss

        • Due to channel fading

  • Required

    • Low transmission distortion


Qos delay

QoS: Delay

  • Offered

    • Circuit Switched

      • usu. low transmission delay

      • Not in sattlelite

    • Packet-switched

      • Variable delay

      • Due to congestion and re-routing in Internet

      • Due to ARQ in wireless comm.

  • Required

    • One-way application

      • Constant delay & low variation

      • e.g. DTV

    • Two-way application

      • Low delay & low variation

      • e.g. Videophone (< 400ms)

    • Interactive

      • Low delay and low feedback delay

      • e.g. VoD TV


2 impact of trans on video coding

2. Impact of trans. on Video coding

  • Data Rate

    • Rate control & output buffering

      • constant bit-rate for circuit-switching network

      • Smoothed bit-rate for packet switching network

    • High activity scene has lower quality

  • Error

    • Error propagation

      • VLC error

        • Bit error => the corresponding VLC decoding error

      • Spatial error propagation

        • VLC error => the successive VLC decoding error

        • Resync. marker for every slices, piictures, GOPs.

      • Temporal error propagation

        • Wrong motion-compensation of Blocks in successive frame


Video transmission system

  • Error-Concealment

    • Use Reversible VLC

    • Use Spatial domain smoothing

      • POCS (projection onto convex set)

    • Use temporal domain: MV estimation

      • Use zero vector from previous frame

      • Use median vector

      • Re-estimation using boundary pixels


Video transmission system

  • Feedback based control

    • Due to low delay requirement

    • Error tracking & intra-coding (H.263 Annex N)

    • Reference picture selection (H.263 Annex U)

intracoding


Video transmission system

  • Delay

    • Delay components

      • Capture delay

        • one frame, but can reduce it

      • Encoder delay

        • Depends on encoder performance, less than one frame

        • B picture introduces extra delay

      • Output buffer

        • Depends on smoothing and rate control

        • Max. out buffer delay = buffer size / tx rate

      • Network delay

        • Depends on network types and network conditions

      • Input buffer

      • Decoding delay

      • Display buffer

    • Low delay case

      • Select appropriate network and QoS negotiation

      • no B picture, low output buffer


3 video transport systems

3. Video Transport Systems

  • MPEG-2 system

    • Provides Multiplexing and synchronization mechanism

      • MPEG-2 = System + Video + Audio

      • Build PS & TS from ES

      • Application environment

      • Fixed, guaranteed bit-rate, predictable delay and predictable errors

      • Used in Digital Cable TV, T/S-DTV, DVD etc

  • Internet Multimedia transport System

    • H.324-based system

      • ITU-T’s Internet conference system

      • Used in Serom’s Dialpad etc

    • RTSP (Real-time Streaming protocol)

      • VCR remocon DESC, SET-UP, PLAY, STOP, TEAR-DOWN

    • SIP

      • simple Session Initiation Protocol, current VoIP

    • RTP

      • transport protocol for multimedia data


Video transmission system

  • PS stream

    • ES (elementary steam) : video bytes, audio bytes streams

    • PES (packetized ES) : timestamped ES packet

    • Program Stream = MPEG-1 system

      • One program (video, audio, etc), no loss assumption

      • Variable and long Packet (called PACK)

      • Pack header includes “SCR (system clock reference)

  • PS stream

encoded audio

encoded audio

PES-1

PES-1

PACK

PACK

encoded video

encoded video

PES-2

PES-2

DVD

PES-3

PES-3

etc

etc


Video transmission system

RS, Conv

PES-1

Program (KBS)

PES-2

TS

tx

Program (MBC)

PES-3

Program map

  • TS (Transport stream)

    • Time stamp and clock info is supported

    • Multiple program is muxed

    • Fixed size (188 Byte) TS packet

    • inner coding (Reed-soloman) and outer coding (convolutional)

    • Program table info is added

RS, Conv

PES-1

TS

PES-2

rx

Program (MBC)

PES-3

Program map


Rtp based transmission

RTP based transmission

  • H.323 system components

    • H.263 terminal

    • Gateway : to PSTN

    • Gatekeeper : call and BW broker

    • MCU: media mixer and trsnscoder

  • H.263 terminal protocol architectures

    • Signaling

    • Data transport


Video transmission system

packet 1

packet 2

Internet

packet 3

00.00

00.01

재생버퍼

00.10

00.08

packet 1

00.14

cam

00.18

00.20

packet 2

00.27

00.28

00.32

packet 3

00.39

00.40

전송 시간

도착 시간

재생 시간

RTP

  • Real time protocol

    • Supports time-stamp, not guarantees the real time transmission

    • “He………llo” is different from “Hell ……..o”


Video transmission system

Ver

P

X

CC

M

PT

Sequence Number

Time-Stamp

Synchronization Source Identifier (SSRC)

Contributing Source Identifier (CSRC)

.

:

Contributing Source Identifier (CSRC)

RTP 의 위상

IP/UDP header

  • RTP Format

    • V: Version (현재 버전은 ‘2’)

    • P: Padding 유/ 무 (‘1’/’0’)

      • 패딩의 마지막 바이트는 패딩의 길이

    • X: 확장 헤더 유/ 무 (‘1’/’0’)

    • CC: Contributor(CSRC ID)의 수 ( 0~15 )

    • M: Marker bit : frame end/ silent period

    • PT: Payload Type

      • Fixed : 0: PCMu Audio, 33: MPEG2 Video

      • Dynamic 97+

(payload header)

Video/audio data


Video transmission system

End system

SSRC=‘9’

PCMu

Audio

Translater

H.261

Mixer

SSRC=’5’

SSRC=’5’

203.246.81.51

CSRC=’9’ / ’15’

G.721 Audio

End system

SSRC=’15’

203.246.81.10

203.246.81.50

203.246.81.54

  • SN (sequence number)

    • 첫번째 패킷- random하게 설정 , 전송시마다 1 씩 증가

  • TS (time-stamp)

    • 첫번째 패킷- random/negotiated value

    • 이전 timestamp값 + 재생되어야 하는 시간 (클럭틱에 의존)

  • SSRC & CSRC

    • Mixing 시에 사용


Video transmission system

200

Sender Report

201

Receiver Report

RTCP

Message types

202

Source Description Message

203

Bye Message

204

Application Specific Message

<Type>

  • RTCP (Real-time control protocol)

    • Help RTP function

    • Use rtp port + 1


Video transmission system

End system

SSRC=‘9’

PCMu

Audio

Translater

H.261

Mixer

SSRC=’5’

SSRC=’5’

203.246.81.51

CSRC=’9’ / ’15’

G.721 Audio

End system

SSRC=’15’

203.246.81.10

203.246.81.50

203.246.81.54

RTCP


Conclusion

Conclusion

  • Congratulation !

    • You have finished

      “From basics, through standard, to application on video coding”

    • The course was not 100% perfect, but ok.

    • I hope you could find any interesting the video coding and information theoretic topics.

    • Any further research cooperation is welcomed.


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