A computer method and apparatus to “digitize” and simulate the classroom lecturing is disclosed. A teacher can use the apparatus to draw on a web page or on a computer whiteboard with extensible size, dynamically insert (delete) image and text objects into (from) the whiteboard or the web page, and record voice narration at the same time. The apparatus stores these activities into a multiplexed data stream and a header stream. The combination of streams and the annotated web page is called an audio-graph (AG) item. Users could save the streams to a file, e-mail it, or upload it to a web site for streamed playback. The apparatus is a system of authoring, playback, organize, and indexing the AG items. The data stream of an AG item comprises (compressed) audio frames, (compressed) stroke frames, image and text frames. The header stream comprises information messages, and event messages (with timing) that are used to control the display (window) during playback. By using event messages and stroke temp files (a text file of strokes), the present invention is able to reduce the delay caused by the pre-processing (1) before user can begin to input voice and stroke during record, or before user can begin to see result during playback. The present invention uses multiple event arrays internally to reduce the frequency and complexity of data stream (file) manipulation during editing (e.g., insert new data stream by record). The system segments the usually very long data stream to many smaller segmented data streams before the AG item is uploaded to the web site. The segmentation information (such as the number of the segments) and the locations are stored in the header stream. The separation of streams to header and segmented data streams enable online playback with little waiting time, even for a very slow and congested network. A group of AG items could be constructed to an AG course. An AG course could be a linked or embedded. A linked AG course is that some of its AG items are stored outside of the AG course file; otherwise it is an embedded AG course. User can save a course to a file, e-mail it or publish to the web site just like a single AG item.
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