RTP Payload Format for Program Cues

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RTP Payload Format for Program Cues
ltdraft-brassil-avt-cues-00.txtgt

• Jack Brassil (HP Labs)
• Henning Schulzrinne (Columbia Univ)
• mailtojtb_at_hpl.hp.com
• December 14, 2000

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Program Cues

• A Program Cue is
• a signaling message used to convey program
  identity, structure and timing
• intended for communicating events whose precise
  timing is significant to receivers (e.g.,
  program start/stop times)
• the building block for a cueing protocol

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Cueing Protocols - Purpose

• Anticipate that both network intermediaries and
  clients will receive and process growing number
  of concurrent RTP streams
• Cues facilitate application creation
• Program recording
• Ad insertion/media personalization
• Program modification (e.g., logo overlay)
• Switching
• Adaptation (e.g., image extraction)
• Notifications (e.g., parental advisorys,
  emergencies)
• Stream monitoring (e.g., DRM)

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Program Notifications in Traditional Broadcast
Media

• Radio Data System (RDS) in VHF/FM
• traffic alerts, program info out-of-band on
  alternate frequencies
• requires RDS-capable radio, often with
  alphanumeric display
• smart receiver can do automatic channel
  switch-over
• Program Delivery Control (PDC)
• Program Identity Labels, start stop times
• carried in teletext
• requires PDC-capable VCR (Gemstars ShowView,
  VideoPlus)
• Local Program Insertion and Pass Thru
• DTMF control channel
• obvious A/V artifacts from poor timing control

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Cueing Protocols Basic Properties

• Cues are always optional in RTP stream
• Each cue is a separate packet (distinguished by
  Payload Type)
• Cues can be added or removed by an intermediary
• Media encoding independence (e.g., PCM, MPEG-4)
• In-band or out-of-band operation
• Compatible with push or pull systems
• Encourage conventions but let application
  developers decide how to construct protocols

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Basic Cue Types

• Event Notification (EN) - indicates start of
  event
• Event Continuing (EC) - event in progress
• Event Termination (ET) - indicates end of event
• Event Pending (EP) - indicates upcoming event

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Proposed Payload Format
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Operational Details

• Redundant notifications are OK
• EN and ET cues should be placed in stream at
  event points
• Applications insert EP and EC as necessary
• Reliability enhancements to RTP apply

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Cueing Protocols Related Activities

• Other less time-sensitive RTP payloads for
  metadata being examined
• Analogous to origin-edge server communication in
  I-CAP
• Some apps possible with other methods of
  synchronization (e.g., SMIL or wall clock time)
• RTP named events

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Cueing Protocols - What works today

• Local transmission of audio as MP3/RTP/IP
  multicast
• Embedded structural cues
• Applications
• track recording service
• third party ad insertion
• Hack encodes SSRC PT fields instead of
  proposed payload so players like WinAmp not
  confused )

ltprogram idgt lttrack 1gt lt/track 1gt
ltad slot 1gt lt/ad slot 1gt
lt/program idgt
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Program Cues - Issues

• Authenticating cues
• Invocation via RTSP
• Identification of Event Types
• Description and announcement via SDP/SAP
• Need for cues to convey program semantics?
• Filters and compatibility with existing apps

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Program Cues - Recommendation

• Sufficient interest to consider standards track
• Need to avoid early adoption of proprietary
  mechanisms
• Interested parties include
• traditional broadcasters
• edge technology providers
• media application developers
• CDNs