Compressed video bitstreams are very sensitive to transmission errors. If we lose packets or receive them with errors during transmission, not only the current frame will be corrupted, but also errors will propagate to succeeding frames. Therefore, we need various mechanisms to protect data and reduce the effects of transmission errors. Error concealment is a data recovery technique that enables the decoder to conceal the effects of transmission errors by predicting the lost or corrupted video data from the previously reconstructed error free information. Motion vector recovery and motion compensation with the estimated motion vector is a good approach to conceal the corrupted macroblock data. In this paper, we show that it is reasonable to use the estimated motion vector to conceal the lost macroblock by providing macroblock distortion models. After we propose a new motion vector recovery algorithm based on optical flow fields, we compare its performance to those of conventional error concealment methods.

In this paper, two low power hardware structures essential for MPEG-4 video codec are proposed for portable applications. First, an adaptive bit resolution control (ABRC) scheme is proposed for a processing element (PE) in a systolic-array type motion estimator (ME). By appropriately modifying the datapath of PE to exploit the correlations in pixel values, its structure is optimized in terms of both hardware cost and low power consumption. As a result, power is saved up to 29% compared with a conventional PE while the computation accuracy is preserved and the overhead is kept negligible. Second, a low power motion compensation (MC) accelerator is proposed. By embedding DRAM whose structure is optimized for low power consumption, the power consumption for external data I/Os is dramatically reduced. In addition, distributed nine-tiled block mapping (DNTBM) with partial activation scheme in the frame buffer reduces the power for accessing frame buffer up to 31% compared to a conventional 1-bank tiled mapping. With the proposed MC accelerator, MPEG-4 SP@L1 decoding system is fabricated using 0.18 µm embedded memory logic (EML) technology.

This paper describes an ultra low power, motion estimation (ME) processor for MPEG2 HDTV resolution video. It adopts a Gradient Descent Search (GDS) algorithm that drastically reduces required computational power to 6 GOPS. A SIMD datapath architecture optimized for the GDS algorithm decreases the clock frequency and operating voltage. A low power 3-port SRAM with a write-disturb-free cell array arrangement is newly designed for image data caches of the processor. The proposed ME processor contains 7-M transistors, integrated in 4.50 mm 3.35 mm area using 0.13 µm CMOS technology. Estimated power consumption is less than 100 mW at 81 MHz@1.0 V. The processor is applicable to a portable HDTV system.

We have developed a low-power, high-performance MPEG-4 codec LSI for mobile video applications. This codec LSI is capable of up to CIF 30-fps encoding, making it suitable for various visual applications. The measured power consumption of the codec core was 9 mW for QCIF 15-fps codec operation and 38 mW for CIF 30-fps encoding. To provide an error-robust MPEG-4 codec, we implemented an error-resilience function in the LSI. We describe the techniques that have enabled low power consumption and high performance and discuss our test results.

This paper proposes a lossless scalable audio coding scheme and quality enhancement processing at the decoder to compensate for some missing scalable units of information. The bit rate scalability is achieved by combining high-compression coding, such as MPEG-4, and horizontal bit slicing of the PCM-coded error signal between the original waveform and the locally reconstructed MPEG-4 signal. The horizontally sliced stream may be transported through an IP network with priority. Even if some units are missing at the decoder, reasonable quality waveform can be reconstructed by means of preserving the important packets. In addition, quality enhancement procedures including scale adjustment and post-processing have been proposed. The scale adjustment eliminates unnecessary zero's, and the post-processing recovers the spectral envelope characteristics of the original input signal. As a result of objective quality evaluation, the two techniques are confirmed to be useful for quality enhancement when lower priority packets are lost. This scheme enables graceful degradation by supporting lossless, near lossless, and high-compression coding within a single scalable framework, and is useful for narrowband to broadband audio streaming.

This paper describes high-quality and processor-efficient software implementation of an MPEG-2 AAC LC Profile encoder. MDCT and quantization processing are accelerated by 21.3% and 19.0%, respectively, through the use of SIMD instructions. In addition, psycho-acoustic analysis in the MDCT domain makes the use of FFTs unnecessary and reduces the computational cost of the analysis by 56.0%. The results of subjective quality tests show that better sound quality is provided by greater efficiency in quantization processing and Huffman coding. All of this results in high-quality and processor-efficient software implementation of an MPEG-2 AAC encoder. Subjective test results show that the sound quality achieved at 96 kb/s/stereo is equivalent to that of MP3 at 128 kb/s/stereo. The encoder works 13 times faster than realtime for stereo encoding on an 800 MHz Pentium III processor.

This paper presents a hardware-efficient architecture of tree-depth scan (TDS) and multiple quantization (MQ) scheme for zerotree coding in MPEG-4 still texture coder. The proposed TDS architecture can achieve its maximal throughput to area ratio and minimize the external memory access with only one wavelet-tree size on-chip buffer. The MQ scheme adopts the power-of-two (POT) quantization to realize a cost-effective hardware implementation. The prototyping chip has been implemented in TSMC 0.35 µm CMOS 1P4M technology. This architecture can handle 30 4-CIF (704576) frames per second with five spatial scalability and five SNR scalability layers at 100 MHz working frequency.

In this letter, we propose a two-stage object-based error-concealment technique for MPEG-2 video transmitted in a burst-packet-loss environment. A burst packet loss typically destroys a large area of MPEG-2 coded video. In the first stage, the missing area is intra-picture estimated and concealed in terms of a region-based approach. In the second stage, irregular-moving objects with respect to the background are identified and compensated from the predictive picture. As compared with conventional concealment approaches, the proposed method achieves better PSNR performance and reduces the visual artifacts.

Advances in broadcast digitization have been rapid in Japan since the broadcasting satellite (BS) digital broadcast services commenced in December 2000. It requires that the receiver, which may also be connected to appliances using a Home Network, has an inbuilt HDD for storing interesting programs. However, it is difficult to guarantee QoS level on a Home Network composed of heterogeneous sub-networks. Therefore, for the purpose of an efficient and appropriate transmission of a video stream, such as MPEG over the Home Network, a new scalable MPEG transmission method is required. For this we propose a Scalability method allowing for Impairments Propagation (SIP), which takes into account the impairments propagated to other frames due to the loss of a macroblock in a given frame. In this paper, we introduce the SIP technique, analyze it mathematically, and evaluate its performance.

A digital watermarking method for moving pictures is proposed in which a watermark can be retrieved from an MPEG bitstream directly. In the proposed method, the watermark is embedded in multiple frames of an original moving picture, and it is detected statistically using multiple frames. Embedding is based on the modification of DCT coefficients that are in the chosen pixel blocks in each video frame. These pixel blocks are chosen differently per video frame in order to avoid regularity and periodicity. The features of the proposed method are that it does not need the original picture nor MPEG decoding processing. The proposed method is evaluated through various attacks including MPEG encoding and StirMark tools. It is shown that the watermark can survive MPEG encoding and frequency domain attacks. The reliability of watermark retrieval is also discussed in terms of statistical test.

This paper proposes a channel monitor-based unequal error protection scheme using a dynamic OFDM subcarrier assignment technique for broadband video transmission systems in frequency selective fading environments. In the proposed system, to achieve stable regeneration of the received video, subcarriers with relatively high channel gain are assigned to the high priority data (HPD) in the MPEG data. To further guarantee a required transmission quality of the HPD, the proposed system also employs subcarrier transmission power control with delay profile information (DPI) feedback-type channel estimation technique. Computer simulation confirms that the proposed technique is effective in preventing quality degradation with about 20 dB lower transmission power than the conventional systems in frequency selective fading environments.

In this paper, we propose an efficient requantization method for INTRA-frames in MPEG-1/MPEG-4 transcoding. The quantizer for an MPEG-1 INTRA block usually uses a quantization weighting matrix, while the quantizer for an MPEG-4 simple profile does not. As a result, the quantization step sizes of the two quantizers may not be the same even for the same quantization parameter. Due to this mismatch in the quantization step size, a transcoded MPEG-4 sequence can suffer from serious quality degradation and the number of bits produced by transcoding increases from the original MPEG-1 video sequence. To solve these problems, an efficient method is proposed to identify a near-optimum reconstruction level in the transcoder. In addition, a Laplacian-model based PDF (probability distribution function) estimation for the original DCT coefficients from an input MPEG-1 bitstream is presented, which is required for the proposed requantization. Experimental results show that the proposed method provides a 0.3-0.7 dB improvement in the PSNR over the conventional method, even at a reduced bit-rate of 3-7%.

A new error correction block based Hybrid ARQ protocol, in which PHY layer packets are composed of multiple error correction blocks, is devised together with a retransmission control scheme constructed on the basis of these error correction blocks. This protocol is designed dedicatedly for mobile AV stations to provide the high quality digital video transmission through a radio channel. To analyze the performance of this protocol, the frame loss rate vs. the uncorrectable error probability is simulated, in comparison with the ordinary packet based retransmission control. A wireless video transmission system using IEEE802.11b PHY is also described, which has been developed with the use of a Medium Access Control (MAC) LSI to perform the proposed protocol.

This paper describes a new approach to the digital watermarking of motion pictures dedicatedly for the MPEG-4 video coding, which intends to enhance the error detection ability. The conventional method lacks not only the detection ability but also the compatibility with video decoders widely used today. Thus in this approach the digital watermarks are to be embedded into the quantized DCT (Discrete Cosine Transform) coefficients for the error detection, where the prevention of the picture quality degradation is also attempted. Experimental results are shown to demonstrate that the error detection ability of the proposed approach is significantly improved, as compared with that of the conventional method, and that the degradation of the picture quality by the watermarking is extremely small.

It has been known that the cell loss ratio (CLR) characteristics of the multiplexed traffic depend on the arrangement of I-picture starting times of individual variable bit rate (VBR) MPEG video sources. In this paper, we propose a simple yet accurate traffic model for the multiplexed VBR MPEG video to calculate the CLR at an ATM multiplexer when the arrangement of the I-picture starting times of individual sources is given. In the proposed model, in order to represent the arrangement of the I-picture starting times, each picture type (I-, P-, or B-picture) of individual source is modeled by the arrival rate histogram, and the multiplexed video traffic is modeled by the convolution of the arrival rate histograms of the pictures that comprise the multiplexed traffic. Using the proposed traffic model, we propose an analytical method to calculate the CLR of the multiplexed VBR MPEG video at an ATM multiplexer. Simulation results show that the proposed method can calculate the CLR more precisely and efficiently than other existing methods.

The advances in services using the present Internet mean that there will be increasing demand for Video on Demand (VoD) on the Internet in the near future. However, because of the best-effort characteristics of the Internet, it is important to suppress the degradation of communication quality caused by packet dropping when Internet traffic is congested. This paper focuses on MPEG transmission over the Internet, and suitable control mechanisms are established for an acceptable Quality of Service (QoS) improvement through detailed evaluation. Packets are classified using a frame-based scheme. The server applies the proposed End-to-End control scheme and shuffles the order of packets to avoid burst dropping, and may omit selected packets belonging to certain frames prior to forwarding. At the intermediate routers, transferred packets are transmitted according to Round Robin (RR) or Weighted Round Robin (WRR) scheduling, and are dropped statistically using selective Random Early Detection (RED) corresponding to frame attributes when there is congestion. We evaluate the proposed performance of transmission method using both computer simulations and empirical measurements of picture quality. The results show that when the traffic volume cannot be estimated in the intermediate routers, the combined use of RR, shuffling and conditional RED is effective, and when the traffic volume can be estimated, the combination of WRR, rate control and RED is effective.

A new method of error concealment for MPEG videos, in which motion vectors are hidden in an MPEG bitstream as a watermark, is proposed in this paper. Several conventional methods conceal error regions by using motion vectors, which are re-estimated in a decoding process. These methods, however, have two problems: (1) The accuracy of a re-estimated motion vector is lower than that of an estimated motion vector in an encoding process. (2) A large amount of calculation is required to re-estimate motion vectors. The proposed method overcomes these problems by using hidden accurate motion vectors. That is, it hides several bits in each 88 DCT block of all frames and, simultaneously, inhibits the image degradation caused by hiding motion vectors. In addition, it has upward compatibility with a standard MPEG decoder and can be combined with conventional methods. Simulation results show that the accuracy of error concealment by the new method is higher than that of the conventional methods.

Scalabilities of bit rate and coding format in coded multimedia contents have become very important for the efficient use of network bandwidth and storage capacity with the recent availability of a wide variety of bandwidth and storage media. However, the conventional approach uses decompression and recompression processes to realize the above scalabilities, which require very expensive computations. In addition, a very large cache space is required for storing the decoded audio-video data. This paper describes three fast scalability methods for MPEG audio and video data, MPEG audio/video bit rate conversion and MPEG format conversion, in order to address these problems. As for the first scalability, MPEG audio coding bit rate conversions, we describe subband domain conversion using bandwidth limitation, requantization and a requantization reflecting phychoacoustic model. Four types of MPEG video bit rate conversion are described that use bandwidth limitation, out-loop requantization, in-loop requantization, and hybrid requantization. As for the format conversion, the fast baseband domain format conversion is performed using coding information such as motion vectors and coding types extracted from input coded video. The experimental results of several comparisons with the above scalabilities and conventional transcoding methods are also shown.

An LSI has been fabricated and measured to demonstrate feasibility of VDD-hopping scheme in an embedded system level by executing MPEG4 CODEC. In the VDD-hopping, supply voltage of a processor is dynamically controlled by a hardware-software cooperative mechanism depending on workload of the processor. When the workload is about a half, the VDD-hopping is shown to reduce power to less than a quarter compared to the conventional fixed-VDD scheme. The power saving is achieved without degrading real-time features of MPEG4 CODEC.

Quantization is an essential step which leads to compression in discrete cosine transform (DCT) domain. In this paper, we show how a statistically non-optimal uniform quantizer can be improved by employing an efficient reconstruction method. For this purpose, we estimate the probability distribution function (PDF) of original DCT coefficients in a decoder. By applying the estimated PDF into the reconstruction process, the dequantization distortion can be reduced. The proposed method can be used practically in any applications where uniform quantizers are used. In particular, it can be used for the quantization scheme of the JPEG and MPEG coding standards.