Dihong Tian

Optimal packet scheduling for wireless video streaming with error-prone feedback

In wireless video transmission, burst packet errors generally produce more catastrophic results than equal number of isolated errors. To miniimize the playback distortion it is crucial for the sender to know the packet errors at the receiver and then optimally schedule next transmissions. Unfortunately, in practice, feedback errors result in inaccurate observations of the receiving status. In this paper, we develop an optimal scheduling framework to minimize the expected distortion by first estimating the receiving status. Then, we jointly consider the source and channel characteristics and optimally choose the packets to transmit. The optimal transmission strategy is computed through a partially observable Markov decision process. The experimental results show that the proposed framework improves the average peak signal-to-noise ratio (PSNR) by 0.6-1.3 dB upon using a traditional system without packet scheduling. Moreover, we show that the proposed method smoothes out the bursty distortion periods and results in less fluctuating PSNR values.

FQM: a fast quality measure for efficient transmission of textured 3D models

In this paper, we propose an efficient transmission method to stream textured 3D models. We develop a bit-allocation algorithm that distributes the bit budget between the geometry and the mapped texture to maximize the quality of the model displayed on the clients screen. Both the geometry and the texture are progressively and independently compressed. The resolutions for the geometry and the texture are selected to maximize the quality for a given bitrate. We further propose a novel and fast quality measure (FQM) to quantify the perceptual fidelity of the simplified model. Experimental results demonstrate the effectiveness of the proposed bit-allocation algorithm using FQM. For example, when the bit budget is 10KB, the quality of the <sc>Zebra</sc> model is improved by 15% using the proposed method compared to distributing the bit budget equally between the geometry and the texture.

BaTex3: Bit Allocation for Progressive Transmission of Textured 3-D Models

The efficient progressive transmission of a textured 3D model, which has a texture image mapped on a geometric mesh, requires careful organization of the bit stream to quickly present high-resolution visualization on the users screen. Bit rates for the mesh and the texture need to be properly balanced so that the decoded model has the best visual fidelity during transmission. This problem is addressed in the paper, and a bit allocation framework is proposed. In particular, the relative importance of the mesh geometry and the texture image on visual fidelity is estimated using a fast quality measure (FQM). Optimal bit distribution between the mesh and the texture is then computed under the criterion of maximizing the quality measured by FQM. Both the quality measure and the bit allocation algorithm are designed with low computation complexity. Empirical studies show that not only the bit allocation framework maximizes the receiving quality of the textured 3D model, but also it does not require sending additional information to indicate bit boundaries between the mesh and the texture in the multiplexed bit stream, which makes the streaming application more robust to bit errors that may occur randomly during transmission.

On-demand transmission of 3D models over lossy networks

Abstract Three-dimensional (3D) meshes are used intensively in distributed graphics applications where model data are transmitted on demand to users’ terminals and rendered for interactive manipulation. For real-time rendering and high-resolution visualization, the transmission system should adapt to both data properties and transport link characteristics while providing scalability to accommodate terminals with disparate rendering capabilities. This paper presents a transmission system using hybrid unequal-error-protection and selective-retransmission for 3D meshes which are encoded with multi-resolutions. Based on the distortion-rate performance of the 3D data, the end-to-end channel statistics and the network parameters, transmission policies that maximize the service quality for a client-specific constraint is determined with linear computation complexity. A TCP-friendly protocol is utilized to further provide performance stability over time as well as bandwidth fairness for parallel flows in the network. Simulation results show the efficacy of the proposed transmission system in reducing transmission latency and providing smooth performance for interactive applications. For example, for a fixed rendering quality, the proposed system achieves 20–30% reduction in transmission latency compared to the system based on 3TP, which is a recently presented 3D application protocol using hybrid TCP and UDP.

Hybrid Variable Length Coding for Image and Video Compression

The conventional run-level variable length coding (RL-VLC), commonly adopted in block-based image and video compression to code quantized transform coefficients, is not efficient in coding consecutive nonzero coefficients. To overcome the deficiency, hybrid variable length coding (HVLC) is proposed in this paper. HVLC takes advantage of the clustered nature of nonzero transform coefficients in the low-frequency (LF) region and the scattered nature of nonzero transform coefficients in the high-frequency (HF) region by employing two types of VLC schemes. A novel two-dimensional position and one-dimensional amplitude coding scheme is proposed to code the LF coefficients while RL-VLC or an equivalent VLC scheme is retained to code the HF coefficients. Experimental results show that HVLC greatly favors the coding of high-resolution, high-complexity scenes, while it preserves low computational complexity.

Hybrid Variable Length Coding in Video Compression using Variable Breakpoint

Hybrid variable length coding (HVLC) was recently proposed as a novel entropy coding scheme for block-based image and video compression, in observation of the inefficiency of the conventional run-level variable length coding scheme in coding consecutive nonzero transform coefficients. In HVLC, each transform block is partitioned into low-frequency and high-frequency regions, and the coefficients in the two regions are coded separately by different schemes. The partition of the transform block was performed based on a predefined, constant breakpoint. In this paper, we propose to partition the transform block using a variable breakpoint that is adaptive to the local context. We present a method to find one optimal breakpoint per transform block or per multi-block partition efficiently, and we show that by using variable breakpoint, the efficiency of HVLC can be improved considerably compared to the constant breakpoint case.

Packetized media streaming over multiple wireless channels

This paper addresses the problem of streaming packetized media through a proxy server to a mobile client over multiple wireless channels. We follow a rate-distortion optimized streaming approach. A real-time sender-driven streaming framework is employed at the proxy server to maximize the playback quality at the client. The experimental results show that the proposed algorithm improves the video quality by 1.3-3dB as compared to the conventional system which simply transmits the video data in the order they are displayed.

Three-dimensional position and amplitude VLC coding in H.264/AVC

Hybrid variable length coding (HVLC) was recently proposed as a novel entropy coding scheme for block-based image and video compression, which divides each transform block into low frequency (LF) region and high frequency (HF) region and codes them differently. To take advantage of the clustered nature of the nonzero coefficients in the LF region, a two-dimensional position and one- dimensional amplitude coding scheme (2DP1DA) was also proposed, which codes the 2D position information, i.e., run of consecutive zero-valued coefficients and run of consecutive nonzero coefficients, jointly by a 2D code table. To further improve the coding efficiency, joint position and amplitude coding is desirable. In this paper, we propose a three-dimensional position and amplitude coding scheme (3DPA) to jointly code the position and amplitude information for each nonzero cluster by a 3D code table. The experimental results show that HVLC with 3DPA for coding LF region achieves about 3.2%~3.7% bit rate reduction for a wide range of quantization parameters (QP) compared with CAVLC in H.264. Moreover, the 3DPA scheme is a compact way to realize the joint position and amplitude coding and it is very suitable for context-adaptive HVLC design.

Joint position and amplitude coding in hybrid variable length coding for video compression

Hybrid variable length coding (HVLC) was recently proposed as a novel entropy coding scheme for block-based image and video compression, which divides each transform block into low frequency (LF) region and high frequency (HF) region and codes them differently. To efficiently code LF region, a two-dimensional position and one-dimensional amplitude coding scheme (2DP1DA) was also proposed, which jointly codes the 2D position information, i.e., run of consecutive zero-valued coefficients and run of consecutive nonzero coefficients. To further explore the potential of HVLC concept, we propose a new scheme for coding LF region, which codes the 2D position and amplitude information of each nonzero cluster jointly with manageable complexity. The experimental results show that compared with CAVLC in H.264, about 3.5% bit rate reduction is achieved by the proposed method for a wide range of quantization parameters (QP).

Progressive streaming of textured 3D models over bandwidth-limited channels

The bitstream of a progressively encoded textured model consists of multiple refinement layers. Decoding each layer produces a model with a simplified mesh and a resolution-reduced texture. We have proposed a quality measure that captures the visual fidelity of the multi-resolution textured models (Tian, D.H. and AlRegib, G., Proc. ACM Multimedia 2004, p.684-91, 2004). Based on that quality measure, we consider the problem of streaming progressively encoded textured models over a bandwidth-limited channel. We develop a bit-allocation algorithm that optimally packetizes the source bits in every transmitted data unit, such that the perceptual quality of the model displayed on the clients screen is maximized. Experimental results confirm the effectiveness of the proposed bit-allocation algorithm.