Shueng Han Gary Chan

Motion Estimation for H.264/AVC using Programmable Graphics Hardware

We present an efficient implementation of motion estimation (ME) for H.264/AVC using programmable graphics hardware. The cost function for ME in H.264/AVC depends on the motion vector (MV) predictor which is the median MV of three neighboring coded blocks. Previous implementations assume no dependency among adjacent blocks, which is not true for H.264/AVC, they also perform unsatisfactorily because of their low arithmetic intensity, which is defined as operation per word transferred. To overcome the dependency problem, we introduce a new implementation which performs ME on block-by-block basis. Moreover, we can adjust the arithmetic intensity easily to optimize the performance on different graphics cards. Experimental results show that our implementation is substantially faster (by 10 times) than our SIMD optimized CPU implementation

BOPPER: Wireless Video Broadcasting with Peer-to-Peer Error Recovery

Wireless digital video broadcasting has experienced much success in years with some industrial systems deployed. We study in this paper how to recover lost packets in video broadcasting by means of a free broadcast-based secondary channel (such as IEEE-802.11 or Bluetooth). In our scheme, termed BOPPER (broadcasting with peer-to-peer error recovery), mobile devices collaboratively help each other to recover packet lost by broadcasting to their neighborhood. BOPPER achieves high scalability, low recovery delay, independence of a backward channel and low bandwidth cost. We study how to minimize the total number of retransmissions while achieving a certain level of recovery capability. We first consider the case with global knowledge (in terms of peer connectivity, loss status and pairwise loss rates of all peers) and formulate the problem as a linear program which can be solved efficiently. The result also serves as the optimum for our distributed protocol. We then propose and study a scalable, adaptive and distributed protocol which makes use of local information and message exchange to achieve efficient packet loss recovery. Simulation results show that our distributed scheme achieves close to the optimum with fast convergence time.

TCP streaming for low-delay wireless video

With the penetration and popularity of mobile devices such as pocket PCs and smart-phones, there is an increasing need of low-delay video streaming over wireless channel. Traditionally, UDP (user datagram protocol) is used for video streaming. However, due to unreliable transmission and fluctuating bandwidth of wireless channel, this requires error concealment and recovery mechanisms which greatly increases the complexity and delay of the system. Furthermore, UDP streams are often more difficult to penetrate firewalls. We hence propose using TCP (transmission control protocol) for video streaming in this paper, due to its ease of use, reliability, and flexibility in selecting frames to transmit. After discussing the wireless system architecture under consideration, we present a multi-worker model as implemented at wireless proxy (or encoder) which handles client requests independently. Our model makes use of a technique (selective packet drop) which selectively drops those unimportant frames so as to maintain video quality and low delay in the presence of congestion and fluctuating bandwidth. We have implemented a cellular and WLAN-based surveillance system using the model, and conduct real network measurement on its performance. Our model is simple and effective for mobile clients of heterogeneous bandwidth and computing power. Our results show that using TCP for streaming leads to good video quality in wireless networks

Low-Complexity Rate Control for Efficient H.263 to H.264/AVC Video Transcoding

Rate control is a complicated problem in the H.264/AVC coding standard, extra computation is usually needed for the existing rate control schemes to estimate the complexity of frames or macroblocks (MBs). However, during transcoding, information from preceded video could be used to simplify the rate control. In this paper, we propose a low-complexity rate control scheme for transcoding from H.263 to H.264/AVC. The relationship between the rate of the pre-coded video and both the rate and distortion of the transcoded video are studied. By using only the rate information from the preceded video, we introduce a row-layer bit allocation and perform average rate shaping across a row of MBs. Estimation error diffusion is also introduced. The proposed scheme has sufficiently lower computational complexity than other methods as there is no explicit complexity measurement of MBs and complicated parameters updating. Experimental results show the effectiveness of the proposed scheme.

Improved refinement search for H.263 to H.264/AVC transcoding based on the minimum cost tendency search

An improved refinement search method for transcoding from H.263 to H.264/AVC is proposed in this paper. Many existing motion re-estimation methods refine the input motion vector (MV) with a small search range, which is usually input MV biased. Motion estimation (ME) in H.263 usually does not consider the rate required for coding the MV, and hence, the input MV may incur a large cost in H.264/AVC. To overcome this problem, we introduce a refinement search method, called minimum cost tendency search (MCTS), which takes the difference between the cost functions for ME in H.263 and H.264/AVC into consideration. The input MV and the predictor MV are used as two anchor points. The proposed MCTS starts searching from the anchor point with a higher cost to another. Finally, the best point is chosen as the center for further refinement. The performance of MCTS is evaluated by comparing with full search, FME in JM software and refinement scheme using small diamond pattern around the input MV (RSD). Experimental results show the proposed MCTS performs more stable than FME and RSD over a wide range of output video quality