Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Patent
1997-09-17
2000-04-25
Vu, Huy D.
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
370394, 370428, 370429, 370503, 395200, H04L 1254, H04J 306, H01J 1300
Patent
active
060552468
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to the addition of time information to data streams such as multimedia data streams, to facilitate editing and replay of the data.
BACKGROUND TO THE INVENTION
Timestamps on multimedia data streams enable time information to be associated with the data representing audio, video or other time dependent media. Recorded streams may require alteration as to rate of play, synchronisation with other streams or editing. The use of timestamps embedded in the streams provides a marker for controlling such operations.
For example timestamps embedded in a data stream can be used to meter the playback rate to ensure that the stream runs at the desired rate. Additionally if several streams are recorded simultaneously and require editing, then operations such as cuts may be required at a particular recorded time on each stream. The use of a timestamp ensures that the cuts can be precisely synchronised.
Timestamps are used within current video tape formats and DAT formats. Timing information in actual time (GMT) is typically laid down with the audio and video streams as they are recorded. Subsequent editing of the streams results in a time track with discontinuities where cuts have been made, and `false` timing data where inserts have occurred, so that during subsequent playback the timestamps do not bear a simple relationship to the times at which the data should be played.
To avoid this a fresh time track may be laid down when editing, with the time at which the edits were made. The original timestamps are thus overwritten so that a new consecutive series of timestamps is available. This approach loses all information about when the original recordings were made, so that additional tracks cannot be synchronised with the edited sequence, further editing will lead to cumulative errors, and recordings cannot be indexed by when they were made.
Instead of timestamping with actual time (GMT), relative timestamps can be used. These are relative times with independent origins and are linked to every data segment (whether audio or video) by the hardware that captures the data. These timestamps often exhibit drift since the electronic clocks in different hardware do not necessarily run with sufficient accuracy. When streams are edited, new sets of relative timestamps are laid down so that the playout software does not have to take care of discontinuities where the edits have been made.
SUMMARY OF THE INVENTION
According to one aspect of the invention a method of adding time information to a data stream comprises the steps of linking first and second timing sequences with the data stream, the first sequence providing a permanent time record of when the data first originated and the second sequence being re-writable when the data stream is changed as during editing, such that time information in the first sequence provides a permanent record of the originating time which is always maintained with any data preserved from the original stream, whilst the second sequence provides an internally consistent timetrack which is updated each time the data stream is changed so as to be consistent with any derivative of the original data stream, for subsequent replay and editing purposes.
The timing sequences may be generated and transmitted with the data stream.
Where the data stream is to be edited "on line", the data stream and timing sequences are preferably buffered before being transmitted to reproduction apparatus.
Where the data stream is to be edited from a recorded condition, the data stream and timing sequences may be recorded in a synchronous or linked manner and the timing sequence information may be embedded in the data stream.
The first and second timing sequences may be embedded into the data stream together or the second timing sequence may be embedded into the data stream after the first timing sequence. Alternatively the timing sequences may be stored separately from the data stream.
In the recorded condition, the second timing sequence may be re-recorded when, and if, the
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Olivetti Research Limited
Phan M.
Vu Huy D.
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