[vod] streaming video over the internet: approaches and
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Streaming Video over the Internet Streaming Video over the Internet Approaches and DirectionsApproaches and Directions
Dapeng WuYiwei Thomas HouWenwu ZhuYa-Qin ZhangJon M. Peha
2001 년 9 월 4 일
발표자 : 서승우
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Raw Video
CompressedAudio
Application-layerQoS ControlCompressed
Video
TransportProtocol
VideoDecoder
AudioDecoder
Raw Audio
VideoCompression
AudioCompression
Application-layerQoS Control
TransportProtocol
MediaSynchronization
Storage Device
Streaming Server
Client/Receiver
Internet(Continuous media distribution services)
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Six Key AreasSix Key Areas
Video Compression Application layer QoS control Continuous media distribution services Streaming servers Media Synchronization mechanisms Protocols for Steaming media
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Two approaches of video compressionTwo approaches of video compression
Nonscalable video coding– Generate 1 compressed bit-stream
Scalable video coding– Generate multiple compressed bit-stream– One is base substream– Others are enhancement substream– SNR , FGS
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Six Key AreasSix Key Areas
Video CompressionApplication layer QoS control Continuous media distribution services Streaming servers Media Synchronization mechanisms Protocols for Steaming media
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Application-Layer QoS ControlApplication-Layer QoS Control
Congestion Control– Rate Control
Source-Based Rate Control
Receiver-Based Rate Control
Hybrid-Rate Control– Rate Shaping
Frame-dropping filter Layer-dropping filter Frequency filter Re quantization filter
Error Control– FEC– Delay-Constrained
Retransmission– Error-Resilient
Encoding– Error-Concealment
To avoid congestion and maximize video quality in the presence of packet loss
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Rate ControlRate Control
Source-Base Rate Control– Probe-Based
Maintain their packet loss ratio below a certain threshold
– Model-Based Based on throughput model
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Rate ControlRate Control
Receiver-Based Rate-Control– When no congestion is detected,join a
layer/channel =>Result in an increase of its receiving rate
– When congestion detected, drops a layer
=> result in a reduction of its receiving rate Hybrid Rate-Control
– Both Sender and receiver control rate
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Rate ShapingRate Shaping
To match the rate of a pre-compressed video bit stream to their target rate constraint
Required for source based rate control
Codec filter Frame-dropping filter Layer-dropping filter Frequency filter Re-quantization filter
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Error ControlError ControlFEC: add redundant informationFEC: add redundant information
Channel coding :– Packetized into k packets– Generate n packet block ( k < n)– Only need to receive any k packets in n packet block
Source coding-based FEC– N-th group of blocks contains redundant information
of (n-1)th group of blocks Joint source/channel coding
– Optimal allocation between source coding and channel coding
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Error ControlError ControlDelay-Constrained RetransmissionDelay-Constrained Retransmission
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Error ControlError ControlError-Resilient EncodingError-Resilient Encoding
MDC : Multiple description coding– Compressed into multiple streams– Each description provides acceptable
visual quality– With only one description, can
reconstruct video with acceptable quality
– COST !!
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Error ControlError ControlError ConcealmentError Concealment
Reconstruct the missing data in intra-coded frames in inter-coded frames
Example of skills– Maximally smooth recovery– projection onto convex sets– various motion vector– coding mode recovery methods
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Six Key AreasSix Key Areas
Video Compression Application layer QoS controlContinuous media distribution service
s Streaming servers Media Synchronization mechanisms Protocols for Steaming media
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Continuous Media Distribution ServicesContinuous Media Distribution Services
Network FilteringApplication-Level MulticastContent Replication
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Network FilteringNetwork Filtering
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Network FilteringNetwork Filtering
Typically, frame-dropping filters are used as network filters
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Application-Level MulticastApplication-Level Multicast
IP multicast has barrier– Scalability,network
management,deployment,support for higher layer functionality
=> application level multicast mechanism was proposed
Media-Bridge– Performs routing at application layer– Interconnect with neighbor Media-Brides through
explicit configuration– Application level multicast is possible
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Content ReplicationContent Replication
Mirroring– Place copies of the original multimedia files
on other machines scattered around the Internet
Caching– Makes local copies of contents that clients
retrieve frequently
– To store complete video is expensive– A few cached frames can contribute to
significant improvement in performance
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Six Key AreasSix Key Areas
Video Compression Application layer QoS control Continuous media distribution servicesStreaming servers Media Synchronization mechanisms Protocols for Steaming media
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Streaming ServersStreaming Servers
Real-Time Operation SystemStorage System
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Streaming ServersStreaming ServersOS:process managementOS:process management
EDF : each task is assigned deadline – close to deadline first
Rate-monotonic scheduling– high rate task first– More task switching
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< EDF vs Rate monotonic >
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Streaming ServersStreaming ServersOS:Resource ManagementOS:Resource Management
Resource management involves admission control and resource allocation
Deterministic admission control– Hard guarantees
Statistical admission control– Statistical guarantees
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Streaming ServersStreaming ServersOS:File ManagementOS:File Management
Non-scatterd vs scattedScatted
– throughput improved– Seek times can be reduced by disk-schedul
ing algorithms SCAN-EDF, grouped sweeping scheduling,DC-SCAN
Support pause/resume,fast forward,fast backward => under study
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Streaming ServersStreaming ServersStorage SystemStorage System
Increase throughput with data striping– load-balance and low latency are two conflicting objectives
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Streaming ServersStreaming ServersStorage SystemStorage System
Increase capacity with tertiary and hierarchical storage– To keep the storage cost down , tertiary
storage must be added
SAN : use fiber channel
NAS : directly attach to a local area network
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Six Key AreasSix Key Areas
Video Compression Application layer QoS control Continuous media distribution services Streaming serversMedia Synchronization mechanisms Protocols for Steaming media
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Media SynchronizationMedia Synchronization
Intra-stream synchronization– Maintain continuity of logical data
unitInter-stream synchronization
– Maintain temporal relationships among different continuous media
Inter-object synchronization– Relation with time-independent data
such as text, still image and streams
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Media SynchronizationMedia Synchronization
Methods maintain the temporal relations– Interval-based– Axes-based : time stamping
Widely used
– Control flow-based– Event-based
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Six Key AreasSix Key Areas
Video Compression Application layer QoS control Continuous media distribution services Streaming servers Media Synchronization mechanismsProtocols for Steaming media
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Protocols For Streaming VideoProtocols For Streaming Video
Transport ProtocolsSession Control Protocols
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Protocols For Steaming VideoProtocols For Steaming VideoTransport ProtocolsTransport Protocols
TCP – retransmission
UDP– Typically employed as the transport
protocol
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Protocols For Steaming VideoProtocols For Steaming VideoTransport ProtocolsTransport Protocols
RTP : does not guarantee QoS or reliable delivery
– Time stamping– Sequence numbering– Payload type identificatio
n– Source identification
RTCP : designed to work in conjunction with RTP
– QoS feedback– Participant identification– Control packets scaling– Inter-media synchronizati
on– Minimal session control i
nformation
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Protocols For Steaming VideoProtocols For Steaming VideoSession Control ProtocolsSession Control Protocols
RTSP– Support VCR-like control operations– (stop,pause/resume,fast forward, fast backward)– Choosing delivery channel(UDT,multicast UDT, TCP)– Establish and control streams of continuous audio and video
media– Media retrieval : media request,ask session setup to server– Adding media to an existing session
SIP– Support user mobility by proxying and redirecting request