1 Type of Question

Task-oriented Question intended to lead to a Recommendation.

2 Motivation

Cable television operators normally receive several programme signals from different local or remote sources, and they switch the appropriate signal at the appointed time, on each output channel of their cable television system to accommodate local advertisements, local programming, emergency messages, etc.

With the advent of digital cable television systems, programme signals take the form of compressed audio-video multiplexes as MPEG-2 bit streams, and cable operators will be confronted with the task to switch among MPEG-2 bit streams, without causing disruptive disturbances to MPEG-2 home decoders, and preferably without incurring the artefacts attendant to multiple cascaded MPEG-2 encoding and decoding.

The problem is compounded by the fact that the various MPEG-2 programme bit streams at the input of a cable system digital program inserter will likely be out of synchronization with each other; they may use different bit rates, different resolutions and different picture formats, and possibly conform to various different profiles of MPEG-2 coding.

The problem is further compounded by the fact that cable operators may wish to edit among MPEG-2 compressed bit streams using some simple visual transitions, such as cross-fades, wipes, etc.

There is also a need to take into account the specific requirements attendant to the possible independent insertion of alternate digital audio and/or data signals that are present in the MPEG-2 multiplex, involving de-multiplexing and re-multiplexing of the MPEG-2 bit streams.

At this time, cable television systems are in transition to digital operation. It is important and urgent to study the operating requirements for local insertion of MPEG-2 bit streams into remote programme bit streams received at cable television head-ends. Cost-effective solutions should be found to meet those requirements, and they should be reflected in any international standardization that may be required in order that those solutions may be readily and uniformly implemented across the industry.

Another important consideration is the replication or reuse of existing analogue functionality in the digital program insertion system. All the attendant monitoring, auditing and control functions in widespread use today should be accommodated in any digital system that supports equivalent applications such as local advertising, local programme insertions, or emergency message insertion.

3 Questions

• What are the functional and operational requirements of the various applications that must be met when inserting different MPEG-2 programme bit streams into the output channel of cable television systems?
• Which technical solutions can be recommended to allow the insertion of different MPEG-2 programme bit streams into the output channel of cable television systems:
• without causing disruptive disturbances to MPEG-2 home decoders;
• without incurring the programme quality losses attendant to repeated MPEG-2 encoding and decoding, while at the same time meeting the specified operating requirements, e.g.
• allowing simple visual transitions between switched programmes,
• allowing independent switching of the video, audio and data present in the MPEG-2 multiplex,


even when the various bit streams:


• are not synchronized to each other,
• use different bit rates and resolutions,
• conform to different MPEG-2 picture formats and profiles?

4 Expected results and anticipated target dates

It is expected that this Question will result in the preparation of a further draft new Recommendation by 2002.

5 Relationships

Cooperation should be established with ITU-R Study Group 6 when appropriate, and with the IEC/ISO in the study of this Question.