To select segments of a media it is necessary to access the media by the selection boundaries. Determining these boundaries for each media can be problematic, and in general segment selection is a difficult task. When a separate index track exists, it becomes possible to create multiple segments of a media for playback by choosing a region of just the index elements. The segment of the index can be copied as it contains references to the real data without copying the original media data. Therefore, when editing, rather than changing the original data for a media to create new segments, a copy of the index can be created. This means that the original data is left untouched and available for use by other users, and the amount of space used is reduced because copying a segment of an index requires far less space than copying a segment of the media. The issue of boundaries is eliminated because there is only index elements to view. Using this technique, arbitrary and overlapping segments of edited material can be created. These new segments are independent of one another. Figure 9.11 shows how multiple sequence tracks can be created for one media source.
Next: Using Indexes For Analysis Up: Indexing Techniques Previous: Using Indexes For Annotations Jon CROWCROFT