1 Motivation
Television transmission operators such as cable television operators and broadcasters 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 television transmission system to accommodate local advertisements, local programming, emergency messages, etc.
With the advent of digital television transmission systems, programme signals take the form of compressed audio-video multiplexes such as MPEG-2 bit streams, and cable operators will be confronted with the task to switch among the bit streams, without causing disruptive disturbances to home decoders, and preferably without incurring the artefacts attendant to multiple cascaded encoding and decoding.
The problem is compounded by the fact that the various programme bit streams at the input of a digital programme 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 or levels of compression coding.
The problem is further compounded by the fact that programme distributers may wish to edit among 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 multiplex, involving de-multiplexing and re-multiplexing of the compressed bit streams.
At this time, television transmission systems are in transition to digital operation. It is important and urgent to study the operating requirements for local insertion of compressed bit streams into remote programme bit streams received at points such as cable television head-ends. Cost-effective and operationally efficient 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.
Another important consideration is the replication or reuse of existing analogue functionality in the digital programme 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 in the analogue domain.
2 Question
Study items to be considered include, but are not limited to the following ones.
What are the functional and operational requirements of the various applications that must be met when inserting different compressed programme bit streams into the output channel of television transmission systems?
Which technical solutions can be recommended to allow the insertion of different compressed programme bit streams into the output channel of television transmission systems:
- without causing disruptive disturbances to home decoders;
- without incurring the programme quality losses attendant to repeated compression 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 compressed bit stream multiplex,
even when the various bit streams:
- are not synchronized to each other,
- use different bit rates and resolutions,
- conform to different picture formats and profiles,
- conform to different compression standards
- are encapsulated in IP streams?
3 Tasks
Tasks include, but are not limited to the preparation of a number of draft new Recommendations by the end of this Study Period.
An up-to-date status of work under this Question is contained in the SG 9 Work Programme.
4 Relationships
-
Cooperation should be established with ITU-T Study Group 16 and ITU-R Study Group 6 when appropriate, and with the IEC/ISO in the study of this Question.
|
