Hiromasa Yanagihara

MPEG audio bit rate scaling on coded data domain

Formerly, once the audio data is compressed, transcoding is used to scale the bit rate, where decoding and re-encoding are taking place. Therefore, data manipulation of coded data has been very complex and time consuming work. We describe three algorithms for bit rate scaling in the coded MPEG data domain. One is a bandwidth limitation method cutting higher frequency components until the target data rate is satisfied. The other two use a re-quantization process where a quantization step in each subband is modified. One of them reflects the psychoacoustic model from bit allocation information obtained in the bitstream in order to improve the bit rate scaling efficiency. The simulation results show that the re-quantization process provides a very high conversion efficiency and a nearly equal sound quality can be obtained as directly coding from PCM by reflecting the psychoacoustic model. It is also shown that a very fast scaling (factor of six) have been achieved when compared with the transcoding method.

A fast scene change detection on MPEG coding parameter domain

This paper proposes a very fast and accurate scene change detection algorithm on MPEG coding parameter domain. The fast operation can be obtained by spatio-temporally subsampling coding information and by exploiting only coding parameters extracted in variable length decoding (VLD) stage, while the accurate detection is accomplished by examining the statistical characteristics of various scene changes on the coding parameter domain. The computer simulation shows that the proposed algorithm can accomplish detection more than 5 times faster than that of real-time playback for MPEG-2 video sequences using a standard workstation. It is also shown that most of abrupt scene changes, dissolve transitions, and wipe transitions have been successfully detected.

MPEG encoding algorithm with scene adaptive dynamic GOP structure

Although a GOP (group of picture) length is often fixed in MPEG, this may not guarantee the best picture quality from the point of view of coding efficiency. Furthermore, it is also well known that P-picture interval M=3 does not provide the best quality for all sequences. We propose an MPEG encoding algorithm with scene adaptive dynamic GOP structure to enhance the picture quality in the cases mentioned above. Using macroblock characteristics such as luminance activity and simple motion compensation on the activity domain, N and M values are dynamically determined.

Moving-object detection from MPEG coded data

We describe a method of moving object detection directly from MPEG coded data. Since motion information in MPEG coded data is determined in terms of coding efficiency point of view, it does not always provide real motion information of objects. We use a wide variety of coding information including motion vectors and DCT coefficients to estimate real object motion. Since such information can be directly obtained from coded bitstream, very fast operation can be expected. Moving objects are detected basically analyzing motion vectors and spatio-temporal correlation of motion in P-, and B-pictures. Moving objects are also detected in intra macroblocks by analyzing coding characteristics of intra macroblocks in P- and B-pictures and by investigating temporal motion continuity in I-pictures. The simulation results show that successful moving object detection has been performed on macroblock level using several test sequences. Since proposed method is very simple and requires much less computational power than the conventional object detection methods, it has a significant advantage as motion analysis tool.

Moving object detection and identification from MPEG coded data

Moving object detection is a useful tool for such purposes as intelligent video browsing/analysis and video surveillance systems. Previously several algorithms have been reported on moving object detection from compressed video data. However, in these algorithms, flat regions are often falsely detected. In addition if multiple moving objects are involved, each moving object may not be identified and therefore object tracking becomes very difficult. We describe a fast moving detection and identification method from MPEG coded data. The experimental results show that each moving object is successfully identified for several surveillance sequences.

One-pass VBR MPEG encoder using scene adaptive dynamic GOP structure

In this paper, we propose an algorithm for one-pass VBR (variable bit rate) MPEG video encoding. We use two techniques to enhance the picture quality in the one-pass VBR coding. One is a scene adaptive dynamic GOP (group of picture) structure control technique according to the picture characteristics estimated by macroblock activity information. The other is a precise bit budget prediction technique for appropriate bit allocation based on the activity and motion characteristics analysis. Since the processing speed of the proposed algorithm is almost equal to that of the conventional CBR (constant bit rate) MPEG encoder, fast VBR encoding can be realized with better picture quality than that of CBR.

Automated MPEG audio-video summarization and description

The paper proposes a novel method for automatically summarizing MPEG coded audio-video content in the compressed domain, and describing audio-video summaries in the MPEG-7 standard format. Semantically important features for summary generation are carefully analyzed, and two types of summaries, digest and highlight, are extracted. A digest extraction is based on an audio level estimation and visual features analysis, where digest shots are adaptively determined for user-specified duration by utilizing the MPEG-7 based motion features. A highlight-based summarization from TV broadcast sports programmes is achieved by analyzing audio class and audio level. The extracted summaries and related features are described by the MPEG-7 description tools. Experimental results show that the digests and highlights can be successfully extracted in various kinds of contents without a priori knowledge of content characteristics.

Shot genre classification using compressed audio-visual features

This paper proposes shot genre classification from MPEG compressed movies, as one of the high-level indexing methods for audio-visual contents. Through statistical analysis of low-level and mid-level audio-visual features on compressed domain, the proposed method can achieve subjectively accurate shot classification within the movies into predefined genre set, which can be applied to various content handling applications, such as summarization, navigation, editing, filtering, and so on. By feeding subjectively evaluated feature set for each shot genre into the linear machine decision tree classifier, each shot is classified at very low cost. The experimental results show that most of the shots in the movies can be classified into subjectively accurate genres, and also the dominant shot genre can correctly resolve each movie genre.

Scalable video decoder and its application to multi-channel multicast system

In this paper, we propose scalable video decoder algorithms using several DCT manipulations such as low pass filtering and resolution conversion in the DCT domain, and their application to a multi-channel multicast system. In the experiment, it has been shown that simultaneous decoding of tens of channels in an ordinary PC can be realized by selecting an appropriate decoding scheme.

A two-stage variable block size motion search algorithm for H.264 encoder

We propose a fast motion search algorithm for H.264 motion estimation with variable block sizes. Motion estimation of H.264 encoder has larger computation complexity than existing video compression standards such as MPEG-4 and H.263 since search steps increase in proportion to the number of block sizes. Here, we employed two-stage motion estimation. In the first stage, 8/spl times/8 to 16/spl times/16 motion estimation is conducted where only the limited areas are searched in 8/spl times/16, 16/spl times/8, and 16/spl times/16 block sizes using the results of 8/spl times/8 block search. Then in the second stage, 4/spl times/4/8/spl times/4/4/spl times/8 block size motion search is performed only when 8/spl times/8 block mode is chosen in the first stage. Using the above two approaches, limited search area and conditional smaller block size search, very fast and highly accurate variable block size motion estimation has been achieved. The experimental results also confirmed that the proposed algorithm can greatly reduce the computational complexity while fully using seven block sizes and maintaining motion estimation efficiency.