RTP Payload Format for Program Cues

Jack Brassil (HP Labs)Henning Schulzrinne (Columbia Univ)

mailto:jtb@hpl.hp.com

December 14, 2000

<draft-brassil-avt-cues-00.txt>

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

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)

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 (Gemstar’s ShowView, VideoPlus+)

Local Program Insertion and Pass Thru DTMF control channel obvious A/V artifacts from poor timing control

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

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

0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |V=2|P|X| CC |M| PT | sequence number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | timestamp | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | synchronization source (SSRC) identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 1: RTP packet header

0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | event type |cuetype| ver | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | duration | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | date | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | time | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | time (cont.) | reserved | label bytecount | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | label | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 2: Payload Format for Cues

Proposed Payload Format

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

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’

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 :)

<program id> <track 1> </track 1> <ad slot 1> </ad slot 1> …</program id>

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

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