The human voice is primarily a carrier of speech, but it also contains non-linguistic features unique to a speaker and indicative of various speaker demographics, e.g. gender, nativity, ethnicity. Such characteristics are helpful cues for audio/video search and retrieval. In this paper, we evaluate the effects of various low-, mid-, and high-level features for effective classification of speaker characteristics. Low-level signal-based features include MFCCs, LPCs, and six spectral features; mid-level statistical features model low-level features; and high-level semantic features are based on selected phonemes in addition to mid-level features. Our data set consists of approximately 76.4 hours of annotated audio with 2786 unique speaker segments used for classification. Quantitative evaluation of our method results in accuracy rates up to 98.6% on our test data for male/female classification using mid-level features and a linear kernel support vector machine. We determine that mid- and high-level features are optimal for identification of speaker characteristics.

We investigate the symmetric Kullback-Leibler (KL2) distance in speaker clustering and its unreported effects for differently-sized feature matrices. Speaker data is represented as Mel frequency cepstral coefficient (MFCC) vectors, and features are compared using the KL2 metric to form clusters of speech segments for each speaker. We make two observations with respect to clustering based on KL2: 1.) The accuracy of clustering is strongly dependent on the absolute lengths of the speech segments and their extracted feature vectors. 2.) The accuracy of the similarity measure strongly degrades with the length of the shorter of the two speech segments. These effects of length can be attributed to the measure of covariance used in KL2. We demonstrate an empirical correction of this sample-size effect that increases clustering accuracy. We draw parallels to two vector quantization-based (VQ) similarity measures, one which exhibits an equivalent effect of sample size, and the second being less influenced by it.

In this paper, we present extensive user studies on browsing and information retrieval in the domain of unstructured videos using the VAST MM video library browser. Our studies were performed over a 3-year period with more than 1,000 participants in the university setting. The majority of students use the video library for retrieval of student presentations in a large engineering design course. Through iterative analysis of context-specific audio, visual, and textual cues, we are able to measure significant improvements on typical retrieval tasks, such as searching for unfamiliar content in a large database with over 300 hours of video. We also present user studies conducted in two videotaped core computer science courses to measure the usefulness of the VAST MM (Video Audio Structure Text MultiMedia) resource for final exam preparation. We find that students who use the lecture video library experience significant improvement in final exam scores.

We introduce a novel and inexpensive approach for the temporal alignment of speech to highly imperfect transcripts from automatic speech recognition (ASR). Transcripts are generated for extended lecture and presentation videos, which in some cases feature more than 30 speakers with different accents, resulting in highly varying transcription qualities. In our approach we detect a subset of phonemes in the speech track, and align them to the sequence of phonemes extracted from the transcript. We report on the results for 4 speech-transcript sets ranging from 22 to 108 minutes. The alignment performance is promising, showing a correct matching of phonemes within 10, 20, 30 second error margins for more than 60 %, 75 %, 90 % of text, respectively, on average. For perfect manually generated transcripts, more than 75 % of text is correctly aligned within 5 seconds.

In the domain of candidly-captured student presentation videos, we examine and evaluate approaches for multimodal analysis and indexing of audio and video. We apply visual segmentation techniques on unedited video to determine likely changes of topics. Speaker segmentation methods are employed to determine individual student appearances, which are linked to extracted headshots to create a visual speaker index. Videos are augmented with time-aligned filtered keywords and phrases from highly inaccurate speech transcripts. An experimental user interface (UI) combines streaming videos, visual, and textual indices for browsing and searching. We evaluate the UI and methods in a large engineering design course. We report on observations and statistics collected over 4 semesters and 598 student participants. Results suggest that our video indexing and retrieval approach is effective, and that our continuous improvements are reflected in an increase in accuracy and completion rates of user study tasks.

We study the problem of semantic concept-based query expansion and re-ranking for multimedia retrieval. In particular, we explore the utility of a fixed lexicon of visual semantic concepts for automatic multimedia retrieval and re-ranking purposes. In this paper, we propose several new approaches for query expansion, in which textual keywords, visual examples, or initial retrieval results are analyzed to identify the most relevant visual concepts for the given query. These concepts are then used to generate additional query results and/or to re-rank an existing set of results. We develop both lexical and statistical approaches for text query expansion, as well as content-based approaches for visual query expansion. In addition, we study several other recently proposed methods for concept-based query expansion. In total, we compare 7 different approaches for expanding queries with visual semantic concepts. They are evaluated using a large video corpus and 39 concept detectors from the TRECVID-2006 video retrieval benchmark. We observe consistent improvement over the baselines for all 7 approaches, leading to an overall performance gain of 77% relative to a text retrieval baseline, and a 31% improvement relative to a state-of-the-art multimodal retrieval baseline.

In the domain of video content retrieval, we present an approach for selecting words and phrases from highly imperfect automatically generated transcripts. Extracted terms are ranked according to their descriptiveness and presented to the user in a multimedia browser interface. We use sense querying from the WordNet lexical database for our method of text selection and ranking. Evaluation of 679 video summarization tasks from 442 users shows that the method of ranking and emphasizing terms according to descriptiveness results in higher accuracy responses in less time compared to the baseline of no ranking.

We present methods for improving text search retrieval of visual multimedia content by applying a set of visual models of semantic concepts from a lexicon of concepts deemed relevant for the collection. Text search is performed via queries of words or fully qualified sentences, and results are returned in the form of ranked video clips. Our approach involves a query expansion stage, in which query terms are compared to the visual concepts for which we independently build classifier models. We leverage a synonym dictionary and WordNet similarities during expansion. Results over each query are aggregated across the expanded terms and ranked. We validate our approach on the TRECVID 2005 broadcast news data with 39 concepts specifically designed for this genre of video. We observe that concept models improve search results by nearly 50% after model-based re-ranking of text-only search. We also observe that purely model-based retrieval significantly outperforms text-based retrieval on non-named entity queries

We investigate methods of segmenting, visualizing, and indexing presentation videos by both audio and visual data. The audio track is segmented by speaker, and augmented with key phrases which are extracted using an Automatic Speech Recognizer (ASR). The video track is segmented by visual dissimilarities and changes in speaker gesturing, and augmented by representative key frames. An interactive user interface combines a visual representation of audio, video, text, key frames, and allows the user to navigate presentation videos. User studies with 176 students of varying knowledge were conducted on 7.5 hours of student presentation video (32 presentations). Tasks included searching for various portions of presentations, both known and unknown to students, and summarizing presentations given the annotations. The results are favorable towards the video summaries and the interface, suggesting faster responses by a factor of 20% compared to having access to the actual video. Accuracy of responses remained the same on average. Follow-up surveys present a number of suggestions towards improving the interface, such as the incorporation of automatic speaker clustering and identification, and the display of an abstract topological view of the presentation. Surveys also show alternative contexts in which students would like to use the tool in the classroom environment.

We present a new method for segmenting, and a new user interface for indexing and visualizing, the semantic content of extended instructional videos. Using various visual filters, key frames are first assigned a media type (board, class, computer, illustration, podium, and sheet). Key frames of media type board and sheet are then clustered based on contents via an algorithm with near-linear cost. A novel user interface, the result of two user studies, displays related topics using icons linked topologically, allowing users to quickly locate semantically related portions of the video. We analyze the accuracy of the segmentation tool on 17 instructional videos, each of which is from 75 to 150 minutes in duration (a total of 40 hours); it exceeds 96%.