Hyeong-Min Nam

Low complexity content-aware video retargeting for mobile devices

In this paper, a low complexity content-aware video retargeting method suitable for mobile multimedia devices is presented. We propose two types of energy functions for intra- and inter-frames to obtain the pixel significance in the video frames. Since the energy functions are defined using only the compressed-domain information such as discrete cosine transform (DCT) coefficients and motion vectors (MVs), instead of fully decoded pixel domain information, the spatiotemporal energy map can be constructed without excessive computations. Based on the proposed energy function, we also introduce a fast seam carving method for mobile devices that carves out the one-dimensional (1-D) seams without annoying artifacts such as jitter and flicker, taking into account the object motion based on MVs. Experimental results show that the proposed video retargeting scheme can achieve high subjective quality with significantly reduced computational loads as compared with existing methods.

Low Complexity H.264 Transcoder for Bitrate Reduction

The paper presents a fast homogenous H.264 video transcoding algorithm in order to reduce the bitrate. We propose a fast mode decision algorithm by using the frame activity based on motion vector (MV) in input bitstream. In the proposed algorithm, the frame activity reflects a degree of macroblock (MB) mode variation between pre-coded bitstream and transcoded bitstream which degrades the rate-distortion (RD) performance significantly due to variable block size in H.264. Experimental results show that the proposed algorithm can be effectively applied to the H.264 video transcoder for the lower complexity and the better quality

Probing-Based Channel Adaptive Video Streaming for Wireless 3G Network

We propose a probing-based channel adaptive video streaming method to provide seamless video transmission over the wireless 3G network. In the proposed method, the available bandwidth (AB) of the end-to-end path is estimated by analyzing RTP packets at the streaming client and the network/client buffer status (NCBS) is predicted by examining the RTCP receiver report (RR) and the application defined packet (APP) including the AB information. Using the estimated AB, the NCBS, and the stored multirate bitstream information, the proposed streaming method determines the next transmission bitrate precisely. Experimental results indicate that the proposed method can be effectively used for video streaming.

Bandwidth estimation based video streaming for mobile devices over HSDPA network

For the seamless video streaming, the bandwidth variation should be considered to control the transmission rate. The packet pair probing technique (PPPT) can be utilized to measure the bandwidth of the network. To adapt the PPPT to the video streaming over the high speed downlink packet access (HSDPA), we experimentally investigate the relationship between the actual available bandwidth (AB) of the HSDPA network and the channel capacity estimated by the PPPT. Using this relationship, we propose an efficient real-time video streaming method. Experimental results show that the proposed method improves the performance of the video streaming over the HSDPA network.

Perceptual quality-complexity optimized video playback on handheld devices

With growing popularity and richer functionality of handheld devices such as PDAs and smart phones, users can enjoy a variety of videos in almost anyplace and anytime. However, since the battery-consumed devices are constrained by limited resources, decoding of full scale video in terms of the frame size and rate is not efficient for handheld devices. This paper presents a low complexity and perceptual quality optimized video playback algorithm. In the proposed method, the best combination of the frame size and rate is determined to maximize the user perceived quality subject to given complexity constraint. According to the selected frame size and rate, the proposed H.264 decoder performs the spatio-temporal rescaling during video playback. Experimental results show that the proposed method reduces the computational complexity significantly while maintaining the acceptable video quality for video playback on handheld devices.

Seamless video streaming for video on demand services in vertical handoff

Vertical handoff is required to achieve anywhere and anytime internet access in the fourth generation (4G) network providing interoperability between universal mobile telecommunications system (UMTS) and wireless LAN (WLAN). However, video data can be lost due to latency caused by vertical handoff. To solve this problem, in this paper, we propose a video streaming method for video on demand (VOD) services that provides seamless playout at the client in vertical handoff. In the proposed method, the streaming server first predicts the network status by using both the channel modelling and the client buffer status and then selects a proper video transmission method for vertical handoff among pre-transmission, post-transmission, and frame-skipping transmission. Performance evaluations are presented to demonstrate the effectiveness of the proposed method.