MPEG-4 Video Bitstream Research Articles

MPEG-4 to H.264 transcoding with frame rate reduction

In this paper, a temporal resolution reduction transcoding method that transforms an MPEG-4 video bitstream into an H.264 video bitstream is proposed. The block modes and motion vectors in the MPEG-4 bitstream are utilized in the H.264 encoder for the block mode conversion and motion vector interpolation methods. Four types of motion vector interpolation methods are proposed in order to avoid the use of brute-force motion estimation in H.264. According to the experimental results, the proposed methods achieve a 3~4 times improvement in the computational complexity compared to the cascade pixel-domain transcoding method, while the PSNR (peak signal to noise ratio) is degraded by 0.2~0.9 dB depending on the bitrates.

An error-resilient GOP structure for robust video transmission

Recent advances in technology have resulted in a significant growth in wireless communications and widespread access to information via the Internet, which have resulted in a strong demand for reliable transmission of video data. The challenge of robust video transmission is to protect the compressed data against hostile channel conditions while bringing little impact on bandwidth efficiency. In motion-compensated video-coding schemes, such as MPEG-1 or MPEG-2, an I frame normally is followed by several P frames and possibly B frames in a group-of-pictures (GOP). In error-prone environments, error happening in the previous frames in a GOP may propagate to all the following frames until the next I frame, which is the beginning of the next GOP. In this paper, we propose a novel GOP structure for robust transmission of MPEG video bitstream. By selecting the optimal position of the I frame in a GOP, robustness can be achieved without reducing any coding efficiency. Another advantage of the proposed GOP structure is also analyzed: compared with the conventional GOP structure, it provides reverse-play operation for MPEG video streaming with much less requirement on the network bandwidth. Experimental results demonstrate both the robustness of the proposed GOP structure and the efficient reverse-play functionality it leads to.

Online Smoothing of VBR H.263 Video for the CDMA2000 and IS-95B Uplinks

The variable bit rate nature of compressed video remains a major challenge to the transmission of real-time video over mobile CDMA cellular networks. Indeed, H.263 and MPEG-4 video bitstreams can exhibit high peak rates and frequent rate variations, which are difficult to support in 2.5G and 3G mobile networks. In this paper, we consider smoothing schemes to minimize the peak rate, variance, and average bandwidth of the transmitted signal, in order to obtain a lower bit-error-rate and thus, a higher received video quality than if unsmoothed video were transmitted. By introducing a delay in the decoding process, the video output stream can be buffered at the video decoder end: this buffering capability is used in order to perform real-time smoothing of the video streams. The transmitter chooses among the set of rates provided by the IS-95B or cdma2000 standards, in a mobility scenario, in order to support the rate variations. We simulate two end-to-end video communication systems based on IS-95B and cdma2000. They consist of an H.263 codec, an H.223 multiplexer, a rate management system and the physical layer components of the IS-95B and cdma2000 standards. The transmitted signal is subject to multipath fading and multiple-access interference, obtained by simulating all the other users in the cell. Results show a significant gain in the video quality obtained through smoothing of the video streams.

A frame-based MPEG characteristics extraction tool and its application in video transcoding

We present a frame-based characteristics extraction tool, which can retrieve meaningful information from MPEG-compressed bitstreams. Taking advantage of the extracted information, we present a general architecture for MPEG video transcoding, which can transcode a given MPEG video bitstream into various MPEG video bitstreams with different characteristics. We also implement an MPEG-2-to-MPEG-4 video transcoder which can not only change the bitstreams' syntax and bitrate but can also encode each semantic video segment as a group of pictures (GOPs), by using the techniques of frame type conversion and video shot boundary detection. Moreover, the proposed transcoder can intelligently select a motion mode for each macroblock of B-VOPs in an MPEG-4 video to avoid some unpredictable artifacts due to mis-selection of the motion mode. This representative application demonstrates the potential usage of such frame-based characteristics.

An efficient error concealment implementation for MPEG-4 video streams

This paper presents an efficient error concealment implementation for damaged MPEG-4 video bitstreams. The chosen spatial and temporal concealment algorithms are designed to fit in real-time decoders and are advantageously combined in a hybrid spatial/temporal approach to provide visually more plausible pictures than basic concealment techniques. In addition, the encoder impact on the visual quality of the reconstruction in presence of channel errors is highlighted.

Wireless MPEG-4 video communication on DSP chips

We discuss the design and implementation of wireless video communication systems on DSPs. We cover both video coding and the channel coding aspects of the problem. The emphasis of the article is on highlighting the issues involved both from an algorithmic standpoint as well as from a DSP standpoint. We discuss the first DSP implementation, to the authors' knowledge, of the MPEG-4 simple profile video standard. We give an overview of DSPs and highlight the salient features that make them especially well-suited for wireless applications. We describe MPEG-4 simple profile video coding noting that in order to facilitate interoperability, it is important that wireless devices use standardized compression algorithms. We discuss our implementation of the MPEG-4 simple profile video codec on Texas Instruments' TMS320C54x DSP and discuss the issues involved. We highlight some general and application-specific DSP instructions on the TMS320C54x DSP that enable us to implement the core operations in the video coder efficiently, often in a single cycle, with minimal control overhead. We describe the performance of MPEG-4 video compression for a variety of content and formats. We give a description of channel coding with the H.223 standard. Then, we describe several channel coding experiments using both unequal and equal protection on MPEG-4 video sent through a simulated GSM channel. Unequal error protection, which ensures fewer errors in the important portions of the MPEG-4 video bitstream, provides improved quality when compared to equal error protection under harsh error conditions.

On end-to-end architecture for transporting MPEG-4 video over the Internet

With the success of the Internet and flexibility of MPEG-4, transporting MPEG-4 video over the Internet is expected to be an important component of many multimedia applications in the near future. Video applications typically have delay and loss requirements, which cannot be adequately supported by the current Internet. Thus, it is a challenging problem to design an efficient MPEG-4 video delivery system that can maximize the perceptual quality while achieving high resource utilization. This paper addresses this problem by presenting an end-to-end architecture for transporting MPEG-4 video over the Internet. We present a framework for transporting MPEG-4 video, which includes source rate adaptation, packetization, feedback control, and error control. The main contributions of this paper are: (1) a feedback control algorithm based on the Real Time Protocol (RTP) and the Real Time Control Protocol (RTCP); (2) an adaptive source-encoding algorithm for MPEG-4 video which is able to adjust the output rate of MPEG-4 video to the desired rate; and (3) an efficient and robust packetization algorithm for MPEG video bit-streams at the sync layer for Internet transport. Simulation results show that our end-to-end transport architecture achieves good perceptual picture quality for MPEG-4 video under low bit-rate and varying network conditions and efficiently utilizes network resources.

A study of the burstiness of combined MPEG video and audio bitstreams

Variable bit rate (VBR) video is very bursty and its transportation over ATM networks is problematic because bandwidth has to be reserved in advance. Studies have shown that VBR video exhibits statistical self-similarity: it displays structural similarities across a wide range of time scales. To date, studies on the burstiness of MPEG compressed bitstreams have been conducted on the video part only; the audio part has been neglected because of its constant bit rate nature. Furthermore, the change in burstiness of MPEG data which occurs after they have been converted to MPEG-2 transport and ATM bitstreams has not been investigated; a considerable amount of overhead bytes is introduced during the conversion. This paper reports on a study on the burstiness of combined MPEG-1 audio and video bitstreams as found on commercial Video CDs, and the burstiness of these combined bitstreams after they have been converted to MPEG-2 transport and ATM layer bitstreams. We found that there is no increase in burstiness in both situations.

An interactive MPEG-1 browsing system

A personal computer (PC) based interactive MPEG-1 browsing system is proposed. The users can get the general information of MPEG video bitstreams, such as the encoding structure and the header parameters of each encoding layer via this browsing system. The users can also get the detailed information of each decoding step. With the aid of the proposed browsing system, users will have the ability to analyze any MPEG-1 bitstream easily. In addition, this system also provides the capability to encode MPEG-1 video bitstreams and to adjust the encoding parameters interactively when the quality of the encoded video is not good enough. The browsing system can also be a useful tool during the development stage of an MPEG encoding or decoding system.