Eenjun Hwang

Querying video libraries

Abstract There is now growing interest in organizing and querying large bodies of video data. In this paper, we will develop a simple SQL-like video language which can be used not only to identify videos in the library that are of interest to the user, but which can also be used to extract, from such a video in a video library, the relevant segments of the video that satisfy the specified query condition. We investigate various types of user requests and show how they are expressed using our query language. We also develop polynomial-time algorithms to process such queries. Furthermore, we show how video presentations may be synthesized in response to a user query. We show how a standard relational database system can be extended in order to handle queries such as those expressed in our language. Based on these principles, we have built a prototype video retrieval system called VIQS. We describe the design and implementation of VIQS and show some sample interactions with VIQS.

Distributed video presentations

Considers a distributed video server environment where video movies need not be stored entirely in one server. Blocks of a video movie are be distributed and replicated over multiple video servers. Customers are served by one video server. This video server, termed the originating server, might have to interact with other servers for downloading missing blocks of the requested movie. We present three types of presentation plans that an originating server can possibly construct for satisfying a customers request. A presentation plan can be considered as a detailed (temporally synchronized) sequence of steps carried out by the originating server for presenting the requested movie to the customer. The creation of presentation plans involves obtaining commitments from other video servers and the network service provider, as well as making local resource commitments, within the limitations of available bandwidth, available buffer and customer consumption rates. For evaluating the goodness of a presentation plan, we introduce two measures of optimality for presentation plans: minimizing the waiting time for a customer and minimizing the access bandwidth. We present algorithms for computing optimal presentation plans and compare their performance experimentally. We have also mathematically proved certain results for the presentation plans.

An event-based model for continuous media data on heterogeneous disk servers

Abstract. Over the last few years, there has been intense work on the problem of retrieval of continuous media (CM) data from disk. However, no single unified framework exists within which such retrieval problems can be studied. In this paper, we first propose a formal model for CM data retrieval from heterogeneous disk servers. This model can be used to characterize CM data retrieval problems independently of how data is laid out on disk, and what objectives (e.g., minimize client delay, maximize buffer utilization, etc.) the system manager is interested in. We then show how using this formal model, we can neatly define what it means to optimally handle events that occur in movie-on-demand (MOD) systems. Examples of such events include new clients entering the system, old clients leaving the system, continuing clients doing pause, rewind and fast-forward operations. Multiple events may occur simultaneously and we show how such events trigger state transitions in the system. We then develop an algorithm called the QuickSOL algorithm that handles events occurring in MOD systems. This algorithm works in two phases: in the first phase, it quickly finds a way of handling as many of the events occurring at time t as possible. In the second phase, it optimizes the solution found in the first phase. The advantage is that the algorithm can be interrupted anytime after the first phase is completed. We report on experiments showing that QuickSOL works well in practice.

Popularity-adaptive index scheme for fast music retrieval

Proliferation of audio databases on the WWW (World Wide Web) necessitates an audio retrieval system to find certain audio content within the audio corpus. Many papers have presented concepts, methodologies and systems to offer users ways to retrieve melody from collections of music contents. In this paper, we present a new index scheme to retrieve music based on the accumulated data of previous user queries to music. We first describe the current status of existing music information retrieval systems, and then present the design and implementation of our prototype system. We report the results obtained from an empirical evaluation of our approach.

Application-Layer Protocol for Collaborative Multimedia Presentations

Many multimedia presentation applications involve retrieval of objects from more than one collaborating server. Presentations of objects from different collaborating servers might be interdependent. For instance, we can consider distributed video servers where blocks of movies are distributed over a set of servers. Here, blocks of a movie from different video servers have to be retrieved and presented continuously without any gaps in the presentation. Such applications first need an estimate of the available network resources to each of the collaborating server in order to identify a schedule for retrieving the objects composing the presentation. A collaborating server can suggest modifications of the retrieval schedule depending on its load. These modifications can potentially affect the retrieval schedule for other collaborating applications. Hence, a sequence of negotiations have to be carried out with the collaborating servers in order to commit for a retrieval schedule of the objects composing the multimedia presentation. In this paper, we propose an application sub-layer protocol, Resource Lock Commit Protocol (RLCP), for handling the negotiation and commitment of the resources required for a collaborative multimedia presentation application.

Protocol for collaborative multimedia presentations

Many multimedia presentation applications involve the retrieval of objects from more than one collaborating server. For instance, we can consider distributed video servers where blocks of movies are distributed over a set of servers. Blocks of a movie from different video servers have to be retrieved and presented continuously without any gaps in the presentation. Such applications first need an estimate of the available network resources to each of the collaborating servers in order to identify a schedule for retrieving the objects composing the presentation. A collaborating server can suggest modifications to the retrieval schedule depending on its load. These modifications can potentially affect the retrieval schedule for other collaborating applications. In this paper, we propose an application sub-layer protocol, the Resource Lock Commit Protocol (RLCP), for handling the negotiation and commitment of the resources required for a collaborative multimedia presentation application.

Unified Read Requests

Most work on multimedia storage systems has assumed that clients will be serviced using a round-robin strategy. The server services the clients in rounds and each client is allocated a time slice within that round. Furthermore, most such algorithms are evaluated on the basis of a tightly specified cost function. This is the basis for well known algorithms such as FCFS, SCAN, SCAN-EDF, etc.In this paper, we describe a Request Merging (RM) module that takes as input, a set of client requests, and a set of constraints on the desired performance such as client waiting time or maximum disk bandwidth, and a cost function. It produces as output, a Unified Read Request (URR), telling the storage server which data items to read, and when the clients would like these data items to be delivered to them. Given a cost function cf, a URR is optimal if there is no other URR satisfying the constraints with a lower cost. We present three algorithms in this paper, each of which accomplishes this kind of request merging. The first algorithm OptURR is guaranteed to produce minimal cost URRs with respect to arbitrary cost functions. In general, the problem of computing an optimal URR is NP-complete, even when only two data objects are considered. To alleviate this problem, we develop two other algorithms, called GreedyURR and FastURR that may produce sub-optimal URRs, but which have some nicer computational properties. We will report on the pros and cons of these algorithms through an experimental evaluation.

Handling Updates and Crashes in VoD Systems

Though there have been several recent efforts to develop disk based video servers, these approaches have all ignored the topic of updates and disk server crashes. In this paper, we present a priority based model for building video servers that handle two classes of events: user events that could include enter, play, pause, rewind, fast-forward, exit, as well assystem events such as insert, delete, server-down, server-up that correspond to uploading new movie blocks onto the disk(s), eliminating existing blocks from the disk(s), and/or experiencing a disk server crash. We will present algorithms to handle such events. Our algorithms are provably correct, and computable in polynomial time. Furthermore, we guarantee that under certain reasonable conditions, continuing clients experience jitter free presentations. We further justify the efficiency of our techniques with a prototype implementation and experimental results.