Wolfgang Effelsberg

Principles of database buffer management

This paper discusses the implementation of a database buffer manager as a component of a DBMS. The interface between calling components of higher system layers and the buffer manager is described; the principal differences between virtual memory paging and database buffer management are outlined; the notion of referencing versus addressing of database pages is introduced; and the concept of fixing pages in the buffer to prevent uncontrolled replacement is explained. Three basic tasks have to be performed by the buffer manager: buffer search, allocation of frames to concurrent transactions, and page replacement. For each of these tasks, implementation alternatives are discussed and illustrated by examples from a performance evaluation project of a CODASYL DBMS.

Automatic audio content analysis

This paper describes the theoretic framework and applications of automatic audio content analysis. Research in multimedia content analysis has so far concentrated on the video domain. We demonstrate the strength of automatic audio content analysis. We explain the algorithms we use, including analysis of amplitude, frequency and pitch, and simulations of human audio perception. These algorithms serve us as tools for further audio content analysis. We use these tools in applications like the segmentation of audio data streams into logical units for further processing, the analysis of music, as well as the recognition of sounds indicative of violence like shots, explosions and cries.

Local-lag and timewarp: providing consistency for replicated continuous applications

In this paper, we investigate how consistency can be established for replicated applications changing their state in reaction to user-initiated operations as well as the passing of time. Typical examples of these applications are networked computer games and distributed virtual environments. We give a formal definition of the terms consistency and correctness for this application class. Based on these definitions, it is shown that an important tradeoff relationship exists between the responsiveness of the application and the appearance of short-term inconsistencies. We propose to exploit the knowledge of this tradeoff by voluntarily decreasing the responsiveness of the application in order to eliminate short-term inconsistencies. This concept is called local-lag. Furthermore, a timewarp scheme is presented that complements local-lag by guaranteeing consistency and correctness for replicated continuous applications. The computational complexity of the timewarp algorithm is determined in theory and practice by examining a simple networked computer game. The timewarp scheme is then compared to the well-known dead-reckoning approach. It is shown that the choice between both schemes is application-dependent.

COMPASS: A probabilistic indoor positioning system based on 802.11 and digital compasses

Positioning systems are one of the key elements required by location-based services. This paper presents the design, implementation and analysis of a positioning system called COMPASS which is based on 802.11-compliant network infrastructure and digital compasses. On the mobile device, COMPASS samples the signal strength values of different access points in its communication range and utilizes the orientation of the user to preselect a subset of the training data. The remaining training data is used by a probabilistic positioning algorithm to determine the position of the user. While prior systems show limited accuracy due to blocking effects caused by the human body, we apply digital compasses to detect the orientations of the users so that we can deal with these blocking effects. After a short period of training our COMPASS system achieves an average error distance of less than 1.65 meters in our experimental environment of 312 square meters.

Abstracting Digital Movies Automatically

Large video on demand databases consisting of thousands of digital movies are not easy to handle: the user must have an attractive means to retrieve his movie of choice. For analog video, movie trailers are produced to allow a quick preview and perhaps stimulate possible buyers. This paper presents techniques to automatically produce such movie abstracts of digtial videos. We define a video abstract to be a sequence of still or moving images presenting the content of a video in such a way that the resprective target groupis rapidly provided with concise information about the content while the essential message of the original is preserved. We therefore mainly distinguish video abstracts consisting of a collection of salient still images and video abstracts consisting of a collection of scenes (sequences of images) which are therefore a video themselves. Still-images abstracting systems have been reported often in the literature. We propose a moving-images abstracting system, called VAbstract, and explain its concept, algorithmic realization and advantages. The paper also describes a series of abstracting experiments in which we compared our automatically produced abstracts to manually produced trailers of TV series.

Automatic recognition of film genres

Film genres in digital video can be detected automatically. In a three-step approach we analyze first the syntactic properties of digital films: color statistics, cut detection, camera motion, object motion and audio. In a second step we use these statistics to derive at a more abstract level film style attributes such as camera panning and zooming, speech and music. These are distinguishing properties for film genres, e.g. newscasts vs. sports vs. commercials. In the third and final step we map the detected style attributes to film genres. Algorithms for the three steps are presented in detail, and we report on initial experience with real videos. It is our goal to automatically classify the large body of existing video for easier access in digital video-on-demand databases.

Automatic text segmentation and text recognition for video indexing

Abstract. Efficient indexing and retrieval of digital video is an important function of video databases. One powerful index for retrieval is the text appearing in them. It enables content-based browsing. We present our new methods for automatic segmentation of text in digital videos. The algorithms we propose make use of typical characteristics of text in videos in order to enable and enhance segmentation performance. The unique features of our approach are the tracking of characters and words over their complete duration of occurrence in a video and the integration of the multiple bitmaps of a character over time into a single bitmap. The output of the text segmentation step is then directly passed to a standard OCR software package in order to translate the segmented text into ASCII. Also, a straightforward indexing and retrieval scheme is introduced. It is used in the experiments to demonstrate that the proposed text segmentation algorithms together with existing text recognition algorithms are suitable for indexing and retrieval of relevant video sequences in and from a video database. Our experimental results are very encouraging and suggest that these algorithms can be used in video retrieval applications as well as to recognize higher level semantics in videos.

Robust camera calibration for sport videos using court models

We propose an automatic camera calibration algorithm for court sports. The obtained camera calibration parameters are required for applications that need to convert positions in the video frame to real-world coordinates or vice versa. Our algorithm uses a model of the arrangement of court lines for calibration. Since the court model can be specified by the user, the algorithm can be applied to a variety of different sports. The algorithm starts with a model initialization step which locates the court in the image without any user assistance or a-priori knowledge about the most probable position. Image pixels are classified as court line pixels if they pass several tests including color and local texture constraints. A Hough transform is applied to extract line elements, forming a set of court line candidates. The subsequent combinatorial search establishes correspondences between lines in the input image and lines from the court model. For the succeeding input frames, an abbreviated calibration algorithm is used, which predicts the camera parameters for the new image and optimizes the parameters using a gradient-descent algorithm. We have conducted experiments on a variety of sport videos (tennis, volleyball, and goal area sequences of soccer games). Video scenes with considerable difficulties were selected to test the robustness of the algorithm. Results show that the algorithm is very robust to occlusions, partial court views, bad lighting conditions, or shadows.

MHEG explained

The upcoming MHEC standard, under development by ISOs Multimedia Hypermedia Experts Group, defines a system-independent encoding of the structure information used for storing, exchanging, and executing multimedia presentations. This article describes the building blocks of an MHEG-encoded presentation through a running example. Our experience involved using MHEG in a networked multimedia kiosk, for which we present a complete MHEG runtime environment. >

The Diver project: interactive digital video repurposing

The digital interactive video exploration and reflection (Diver) system lets users create virtual pathways through existing video content using a virtual camera and an annotation window for commentary. Users can post their Dives to the WebDiver server system to generate active collaboration, further repurposing, and discussion. Although our current work focuses on video records in learning research and educational practices, Diver can aid collaborative analysis of a broad array of visual data records, including simulations, 2D and 3D animations, and static works of art, photography, and text. In addition to the social and behavioral sciences, substantive application areas include medical visualization, astronomic data or cosmological models, military satellite intelligence, and ethnology and animal behavior. Diver-style user-centered video repurposing might also prove compelling for popular media with commercial application involving sports events, movies, television shows, and video gaming. Future technical development includes possible enhancements to the interface to support simultaneous display of multiple Dives on the same source content, a more fluid two-way relation between desktop Diver and WebDiver, and solutions to the current limitations on displaying and authoring time/space cropped videos in a browser context. These developments support the tools fundamentally collaborative, communication-oriented nature.