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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
slide8
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
slide9
Feedback based control
    • Due to low delay requirement
    • Error tracking & intra-coding (H.263 Annex N)
    • Reference picture selection (H.263 Annex U)

intracoding

slide10
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
slide12
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

slide13

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
slide15

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”
slide16

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

slide17

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
slide18

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
slide19

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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