Feedback techniques for continuity and synchronization in multimedia information retrieval

Abstract

Future advances in storage and networking technologies will make it feasible to build multimedia on-demand information servers capable of providing services similar to those of a neighborhood videotape rental store over metropolitan area networks. Such multimedia information servers must not only support retrieval of continuous media units (such as video frames and audio samples), but also preserve synchrony among playback of the different media components constituting a multimedia object. We develop techniques for supporting continuous and synchronous retrieval from multimedia servers. We present feedback techniques by which, during retrieval of multimedia objects from a multimedia server to mediaphones, the multimedia server uses lightweight messages called feedback units transmitted periodically back to it (by mediaphones) to detect impending discontinuities as well as asynchronies at mediaphones. The multimedia server then preventively readjusts media transmission so as to avoid either anomaly, and steers the mediaphones back to synchrony. Given the available buffer sizes at mediaphones and the maximum tolerable asynchrony, we present methods to determine the minimum rate at which feedback units must be transmitted so as to maintain both continuity and synchronization. These feedback techniques remain robust even in the presence of playback rate mismatches and network delay jitter, and their initial simulation for video-audio playback yields a feedback rate of one per 1,000 media units to keep the asynchrony within 250ms, showing that the overhead due to feedback transmission is very small. The constant rate feedback techniques developed in this article form the basis of a prototype on-demand information server being developed at the UCSD Multimedia Laboratory.

Negotiation for automated generation of temporal multimedia presentations

“…In their unified overview of low-level multimedia synchronization, Steinmetz and Nahrstedt [24] present a four-layer synchronization reference model, an overview of multimedia synchronization approaches, and an account of multimedia presentation requirements; they focus on multimedia synchronization issues for stored multimedia systems. Research on network and operating system synchronization issues, such as feedback techniques and protocols for intermedia synchronization given network jitter (e.g., [18,19,20]), also falls within this category. In MAGIC, conceptual objects are generated dynamically, so object duration information and inter-object synchronization points can rarely be stored or computed prior to the generation of a presentation plan.…”

Managing adaptive presentation executions in distributed multimedia database systems

“…Little and Ghafoor proposed an adaptive scheduling mechanism [6]. Rangan et al [9] described the use of lightweight messages, called feedback units which are transmitted periodically back to media servers to detect impending discontinuities as well as asynchronies at so-called mediaphones. In contrast, in our approach the central database environment receives only feedback messages from the presentation sites when a system reaction is necessary to resolve lacking or left-over system performance.…”

Especificación y evaluación de un algoritmo de sincronización de grupo de flujos multimedia

“…En [RAN92], [RAM92] y, posteriormente, en [RAM93], [RAM93b], [RAM95], [RAN95a] y [RAN95b], se presenta el concepto de servidor multimedia bajo demanda y los requisitos de un servicio multimedia bajo demanda. Formula el problema de mantener la continuidad de la reproducción de cada flujo en presencia de múltiples peticiones de los suscriptores y presenta algoritmos de control de admisión que permiten a un servidor satisfacer el máximo número de suscriptores simultáneo posible.…”

“…Es conveniente que las tareas que realicen estos dispositivos sean lo más simples y sencillas posibles para no tener que incrementar las prestaciones y la complejidad asociada. [RAN95b]) permitía utilizar dispositivos receptores sencillos (llamados mediáfonos). Sin embargo, el algoritmo propuesto, requiere que los dispositivos reproductores realicen alguna tarea adicional pero, en cualquier caso, también se puede implementar con dispositivos sencillos, con el hardware necesario (por ejemplo, tarjeta de sonido con los correspondientes altavoces, el monitor o pantalla, etc.…”

“…Mientras que en el protocolo Feedback ( [RAN92], [RAM92], [RAM93], [RAM93b], [RAN95a], [RAN95b]) el jitter introducía un error, en el algoritmo propuesto en la presente Tesis no se produce dicho error. Por otra parte, dependiendo del tipo de aplicación, el error producido por el protocolo de tiempo global NTP podrá despreciarse, por ser de unos pocos milisegundos.…”