One of the fundamental challenges in deploying multimedia systems, such as telemedicine, education, space endeavors, marketing, crisis management, transportation, and military, is to deliver smooth and uninterruptible flow of audio-visual information, anytime and anywhere. A multimedia system may consist of various devices (PCs, laptops, PDAs, smart phones, etc.) interconnected via heterogeneous wireline and wireless networks. In such systems, multimedia content originally authored and compressed with a certain format may need bit rate adjustment and format conversion in order to allow access by receiving devices with diverse capabilities (display, memory, processing, decoder). Thus, a transcoding mechanism is required to make the content adaptive to the capabilities of diverse networks and client devices. A video transcoder can perform several additional functions. For example, if the bandwidth required for a particular video is fluctuating due to congestion or other causes, a transcoder can provide fine and dynamic adjustments in the bit rate of the video bitstream in the compressed domain without imposing additional functional requirements in the decoder. In addition, a video transcoder can change the coding parameters of the compressed video, adjust spatial and temporal resolution, and modify the video content and/or the coding standard used. This paper provides an overview of several video transcoding techniques and some of the related research issues. We introduce some of the basic concepts of video transcoding, and then review and contrast various approaches while highlighting critical research issues. We propose solutions to some of these research issues, and identify possible research directions.

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Video transcoding: an overview of various techniques and research issues

The browsing of quality videos on small hand-held devices is a common scenario in pervasive media environments. In this paper, we propose a novel framework for video adaptation based on content recomposition. Our objective is to provide effective small size videos which emphasize the important aspects of a scene while faithfully retaining the background context. That is achieved by explicitly separating the manipulation of different video objects. A generic video attention model is developed to extract user-interest objects, in which a high-level combination strategy is proposed for fusing the adopted three types of visual attention features: intensity, color, and motion. Based on the knowledge of media aesthetics, a set of aesthetic criteria is presented. Accordingly, these objects are well reintegrated with the direct-resized background to optimally match the specific screen sizes. Experimental results demonstrate the efficiency and effectiveness of our approach

Video Adaptation for Small Display Based on Content Recomposition

In recent years, blogging has become an exploding passion among Internet communities. By combining the grassroots blogging with the richness of expression available in video, videoblogs (vlogs for short) will be a powerful new media adjunct to our existing televised news sources. Vlogs have gained much attention worldwide, especially with Google's acquisition of YouTube. This article presents a comprehensive survey of videoblogging (vlogging for short) as a new technological trend. We first summarize the technological challenges for vlogging as four key issues that need to be answered. Along with their respective possibilities, we give a review of the currently available techniques and tools supporting vlogging, and envision emerging technological directions for future vlogging. Several multimedia technologies are introduced to empower vlogging technology with better scalability, interactivity, searchability, and accessability, and to potentially reduce the legal, economic, and moral risks of vlogging applications. We also make an in-depth investigation of various vlog mining topics from a research perspective and present several incentive applications such as user-targeted video advertising and collective intelligence gaming. We believe that vlogging and its applications will bring new opportunities and drives to the research in related fields.

Vlogging: A survey of videoblogging technology on the web

In this article, we investigate using multi-core graphics processing units (GPUs) for video encoding and decoding. After an overview of video coding and GPUs, we review some previous work on structuring video coding modules so that the massive parallel processing capability of GPUs can be harnessed. We also review previous work on partitioning the video decoding flow between the central processing unit (CPU) and GPU. After that, we discuss in detail a GPU based fast motion estimation to illustrate some design considerations in using GPUs for video coding, and the tradeoff between speedup and rate-distortion performance. Our results highlight the importance to expose as much data parallelism as possible in designing algorithms for GPUs.

Video Coding on Multicore Graphics Processors

Systems and methods are provided for performing transcoding in video communication system that use scalable video coding. The systems and methods can be used to transcode or convert input signals having certain characteristics into desired output signals having different characteristics requirements. The systems and methods are based on compressed domain processing, partial decoding-reencoding, or full decoding-reencoding with side information, depending on the specific characteristics of the input and desired output signals.

System And Method For Transcoding Between Scalable And Non-Scalable Video Codecs

In order to obtain optimal visual quality while meeting the bit rate requirements, a video transcoder needs efficient rate-control with fine and dynamic adjustments. This paper proposes a new frequency domain complexity estimation scheme and an algorithm for adaptive bit allocation during transcoding. In conjunction with frame skipping mechanism, the proposed algorithm adaptively determines spatial coding parameters to realize very low target bitrate for MPEG-2 to MPEG-4 transcoding. Experiments show that the proposed algorithm performs accurate target bit rate transcoding, improves the visual quality and effectively alleviates visual quality degradation during scene changes.

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Low delay rate-control in video transcoding

In this paper, we consider the problem of MPEG-4 visual simple profile to H.264/AVC baseline profile (BP) transcoding. An efficient transcoding algorithm with fast mode selection and motion vector refinement is proposed. The proposed algorithm exploits the side information from the decoding stage to predict the coding modes and MVs of H.264/AVC BP coding. The proposed algorithm consists of two parts: INTRA macroblocks (MBs) transcoding and INTER MBs transcoding. By reusing the side information during the decoding stage, these techniques provide significant complexity reduction, when compared with the fully spatial domain approach.

MPEG-4 to H.264/AVC transcoding

Video scenes containing multiple objects can potentially achieve higher degree of compression and better visual quality with individual coding for each object. Video objects are not always synchronous, implying each object may have a separate temporal resolution. This paper proposes a rate control algorithm for multiple video object encoding. Using a novel bit allocation strategy, the algorithm achieves accurate target bit rate, provides good visual quality, and decreases buffer overflow/underflow. Experimental results for both synchronous and asynchronous multiple video object encoding demonstrate that, when compared with the existing rate control scheme recommended by the MPEG-4 standard, the proposed algorithm provide better temporal-spatial tradeoff with more accurate rate regulation.

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Synchronous and asynchronous multiple object rate control for MPEG-4 video coding

Exploitation of redundancies for superior coding efficiency is one of the major research issues in multi-view video coding (MVC). However, this incurs extra computation, counteracting the benefit gained from coding efficiency. This paper exploits inter-view correlations among video objects and background to lower the prediction complexity while achieving high coding efficiency in MVC. We propose an effective object-based scheme that utilizes video object information obtained from the coded base view. This information assists to predict disparity vectors and motion vectors in enhancement views (EVs) by employing object registration and warping. This leads to high compression and low-complexity coding scheme for EVs. The proposed scheme provides higher coding efficiency when compared to the segmentation-free scheme, while achieving lower computational complexity.

Xiaohui Wei

Papers

Video transcoding: an overview of various techniques and research issues

Low delay rate-control in video transcoding

MPEG-4 to H.264/AVC transcoding

Synchronous and asynchronous multiple object rate control for MPEG-4 video coding

Lowering the Complexity of Multi-view Encoding through Dynamic Segmentation and Registration of Video Object