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A Multimedia Recording Server

To allow easy deployment, the interface to playback systems should be made compatible with WWW browsers, such as Mosaic or Netscape. This enables the media to be selected and replayed using a GUI, and this approach avoids writing a special playback client but requires the server playback interface to look like a WWW server. However, using a naive approach, the user is able to playback the whole conference, but is not able to select their own start point or end point.

Many of the problems associated with the delivery of multimedia to end-users are issues of synchronisation. It has become apparent that synchronisation is more complicated than one may think. We have determined that there are at least three kinds of synchronisation that are important for media synchronisation. They are:

lip synchronisation

where the movement of the lips as seen on the video and the delivery of the audio persuade the user that the person is really speaking at that time.

time synchronisation

where a specification of time, either relative or absolute, goes to the same point in time in each stream of each media, regardless of the volume of data in the streams.

inter-packet synchronisation

where packets are presented to the network, by a player, in such a way that they arrive at the media tools in the same order and inter-packet gap as when they arrived at a recorder. Where more than one stream is being played some kind of inter stream multiplexing is required to maintain this synchronisation.

It is desirable to have a unified approach which makes the tasks of recording and playback simple to achieve, and overcomes the problems just discussed. By considering the problems of the existing tools, it is apparent that a system that does recording and playback must have:

a tool for recording multiple media within the same conference
a tool for playing multiple media into a new conference
user specifiable streams on recording or playback
synchronisation between the media streams
a single point of contact for accessing the recordings
a large repository of disc space for the recordings

next up previous contents
Next: Server Interfaces Up: Recording Previous: Reliable Multicast