1507754
A compressed-domain heterogeneous video transcoder
The forthcoming multimedia telecommunication services are expected to use pre-encoded videos for storage and transmission. The heterogeneities of the present communication networks and the clients' devices demand matching the encoding format of the video source to the constraints of the networks and clients' devices. In order to provide quality support services to heterogeneous clients or transmission channels, the video server should have the capability of performing heterogeneous transcoding, which is regarded as a process of converting a previously compressed video bitstream into another bitstream with a different format. However, much investigation has been conducted to focus on homogeneous transcoding. Only a limited number of methods have been proposed to realize the heterogeneous transcoding from MPEG-2 to H.263. The major difficulties for transcoding B-picture to P-picture is that the incoming DCT coefficients arc predicted from the forward and backward prediction. In other words, the DCT coefficients predicted from the previous frame is not available. Therefore, the required new prediction errors need to be reestimated in the pixel domain. This process involves high computational complexity as well as introduces reencoding errors. Motivated by this, we propose a new transcoder architecture to convert a B-picture into a P-picture by making use of the techniques of motion compensation in the DCT domain and indirect addition of DCT coefficients. In this paper, we derive a set of equations and formulate the problem of how to obtain the DCT coefficients. Experimental results show that the proposed video transcoder achieve a better performance as compared to the conventional video transcoder in terms of both quality and complexity. Furthermore, we propose a fast algorithm to speed up the transcoding process making use of the correlation of motion activities between pictures.
6180081
New adaptive partial distortion search using clustered pixel matching error characteristic
The partial distortion search is a particularly attractive fast block-matching algorithm, because it introduces no prediction error as compared with the full-search algorithm. It reduces the number of necessary matching evaluations for every searching point to save computation. In the literature, many researches have tried to improve block-matching algorithms by making use of an assumption that pixels with larger gradient magnitudes have larger matching errors on average. Based on a simple analysis, we have found that on average, pixel matching errors with similar magnitudes tend to appear in clusters for natural video sequences. By using this clustering characteristic, we propose an adaptive partial distortion search algorithm which significantly improves the computational efficiency of the original PDS. This approach is much better than other pixel gradient based adaptive PDS algorithms. In addition, our proposed algorithm is suitable for motion estimation of both opaque and boundary macroblocks of an arbitrary shaped object in MPEG-4 coding.
10358457
A new adaptive interframe transform coding using directional classification
Interframe transform coding is affected not only by the statistics of spatial details within a frame, but also by the variation of the amount of movement and other temporal activities in different regions of the image sequence. Therefore, adaptive techniques have to be used in order to achieve good image quality. In this paper, we propose a new version of the adaptive interframe coding method, namely directional classification, which is based on image sequence statistics. Blocks with different perceptual features such as edges and high motion activity are categorised to different classes. Then, a new adaptive quantization, associated with appropriate scanning and Huffman coding, are employed based on the classification map. Coding tests using computer simulation show this technique is indeed very efficient.<<ETX>>
3198744
Dynamic frame skipping for high-performance transcoding
Transcoding is a process of converting a previously compressed video bitstream into a lower bit-rate bitstream. When some incoming frames are dropped for the frame-rate conversion in transcoding, the newly quantized DCT coefficients of prediction error need to be re-computed, which can create an undesirable complexity as well as introduce re-encoding error. We propose a new architecture for a frame-skipping transcoder to improve picture quality and to reduce complexity. It is observed that re-encoding error is reduced significantly when the strategy of direct summation of DCT coefficients and the error compensation feedback loop are employed. Furthermore, we propose a frame-rate control scheme which can dynamically adjust the number of skipped frames according to the incoming motion vectors and the re-encoding error due to transcoding such that the decoded sequence can have smooth motion as well as better transcoded pictures. Experimental results show that, as compared to the conventional transcoder, the new frame-skipping transcoder is more robust, produces smaller requantization errors, and has simple computational complexity.
841469
Variable temporal-length 3-D discrete cosine transform coding
Three-dimensional discrete cosine transform (3-D DCT) coding has the advantage of reducing the interframe redundancy among a number of consecutive frames, while the motion compensation technique can only reduce the redundancy of at most two frames. However, the performance of the 3-D DCT coding will be degraded for complex scenes with a greater amount of motion. This paper presents a 3-D DCT coding with a variable temporal length that is determined by the scene change detector. Our idea is to let the motion activity in each block be very low, while the efficiency of the 3-D DCT coding could be increased. Experimental results show that this technique is indeed very efficient. The present approach has substantial improvement over the conventional fixed-length 3-D DCT coding and is also better than that of the Moving Picture Expert Group (MPEG) coding.
8897506
New architecture for dynamic frame-skipping transcoder
Transcoding is a key technique for reducing the bit rate of a previously compressed video signal. A high transcoding ratio may result in an unacceptable picture quality when the full frame rate of the incoming video bitstream is used. Frame skipping is often used as an efficient scheme to allocate more bits to the representative frames, so that an acceptable quality for each frame can be maintained. However, the skipped frame must be decompressed completely, which might act as a reference frame to nonskipped frames for reconstruction. The newly quantized discrete cosine transform (DCT) coefficients of the prediction errors need to be re-computed for the nonskipped frame with reference to the previous nonskipped frame; this can create undesirable complexity as well as introduce re-encoding errors. In this paper, we propose new algorithms and a novel architecture for frame-rate reduction to improve picture quality and to reduce complexity. The proposed architecture is mainly performed on the DCT domain to achieve a transcoder with low complexity. With the direct addition of DCT coefficients and an error compensation feedback loop, re-encoding errors are reduced significantly. Furthermore, we propose a frame-rate control scheme which can dynamically adjust the number of skipped frames according to the incoming motion vectors and re-encoding errors due to transcoding such that the decoded sequence can have a smooth motion as well as better transcoded pictures. Experimental results show that, as compared to the conventional transcoder, the new architecture for frame-skipping transcoder is more robust, produces fewer requantization errors, and has reduced computational complexity.
10812167
A TCP-Friendly Stateless AQM Scheme for Fair Bandwidth Allocation
Queue management, bandwidth share, and congestion control are very important to both robustness and fairness of the Internet. In this article, we investigate the problem of providing a fair bandwidth allocation to those flows that share congested link in a router. A new TCP-friendly router-based AQM (active queue management) scheme, termed WARD, is proposed to approximate the fair queueing policy. WARD is a simple packet dropping algorithm with a random mechanism, and discriminates against the flows which transmit more packets than allowed. By doing this, it not only protects TCP connections from UDP flows, but also solves the problem of competing bandwidth among different TCP versions such as TCP Vegas and Reno. In addition, WARD works quite well for TCP flow isolation even with different round trip times. In other words, WARD improves the unfair bandwidth allocation properties. Furthermore, it is stateless and easy to implement, so WARD controls unresponsive or misbehaving flows with a minimum overhead
7668661
Evaluation on security and privacy of Web-based learning systems
Web-based learning systems are becoming popular in the recent years. Many courses and lectures are now conducted online. Similar to other Web-based applications, security and privacy of Web-based learning systems should not be overlooked. We evaluate the security and privacy of general Web-based learning systems. We address the security and privacy requirements specific to them. Recommendations on design and implementation of a secure Web-based learning system are also presented. In particular, we have evaluated the security services of two popular Web-based learning tools.
9759416
Mobile learning: a new paradigm in electronic learning
As mobile phones become popular, with many people being able to afford them, the demand for mobility is extended to teaching and learning purposes. One recent and significant change in learning environments is the demand for mobility. We introduce a proposed framework of mobile learning. It consists of four functional levels: (1) mobile learning applications, (2) mobile user infrastructure, (3) mobile protocol and (4) mobile network infrastructure. The framework can simplify the design and development so that different parties (e.g. vendors, service providers, designers, developers) can address individual levels. A single party can build on functionalities provided by others. The functions of these four levels are described with some examples. Moreover, practical knowledge management and learning community are two major issues in mobile learning.
894881
Performance improvement of TCP Vegas over heterogeneous networks
Current IP network has become the dominant paradigm for all networking environments. The significant cause of packet losses in such heterogenous networks is no longer limited to network congestion. Traditional TCP interprets every packet loss as caused by congestion which may be not the case in the current Internet. Misinterpretation of wireless random loss as an indication of network congestion results in TCP slowing down its sending rate unnecessarily. We propose a new variant of TCP Vegas named RedVegas. By using the innate nature of Vegas and congestion indications marked by routers, RedVegas may detect random packet losses precisely. Through the packet loss differentiation, RedVegas reacts appropriately to the losses, and therefore the throughput of connection over heterogeneous networks can be significantly improved.
35179919
WebQuest Markup Language (WQML) for Sharable Inquiry-Based Learning
WebQuest is a model for constructivist inquiry-based learning in which the information used by learners is collected from the Web. A WebQuest exists in form of a Web site that contains a defined set of componential Web pages. In this paper, we specify the WebQuest Markup Language (WQML) for WebQuest construction. WQML enables WebQuests to be implemented as sharable courseware objects and thus to be interoperable with most learning management systems (LMS).