Differences between Various Video Coding Standards - Essay Example

Differences of H.261, H.263, MPEG-1, and MPEG-2 video coding standards Abstract Video compression allows for the reducing of data that is used to present video images. This article deals with four formats of video encoding standards, namely H.261, H.263, MPEG-1, and MPEG-2 video coding standards. We are going to understand each standard, deriving similarities, and differences as well as find out how they work. This article will elaborate how these standards enable images to be changed into a motion picture. We will come to realize that these standards have evolved over time to accommodate faster better methods for encoding motion picture. For example, H.261 as a standard for video coding is also known as MPEG-1. It was initialized in 1988. This was the first member of the H.26x group of standards. H.263 was designed for low bit rate compressed standards for video conferencing. It has evolved into the use for flash video display. H.263 was an evolution from H.261, as well as the MPEG-1 and MPEG-2 standards. It was initially completed in the year 1995 and provided a replacement for the H.261 at all bit rates. MPEG-1 on the other hand, is used for lossy compression of video & audio. It compresses down to 1.5 Mbit / s for raw digital video and audio. Its development began in 1988, and was finished in 1992, then published a few months later. MPEG-2 evolved from MPEG-1. It is mainly used as the format for digital TV sent over the air (terrestrial). It is also used to specify the format for movies as well as programs that are on DVDs. It was deployed by the Moving Pictures Expert Group (MPEG). It eventually grew to become an international standard. A clear difference of these video coding standards will be discussed in this paper. Introduction There are several video coding standards that exist and they were developed to fit various applications. A few of these standards will be discussed in details, outlining their differences and their suitability to particular applications. The standards in question here are: H.261, H.263, MPEG-1 and MPEG-2. Characteristics of the Video Coding Standards H.261 This is an early video coding/compression standard and it uses the principle of motion-compensation based compression thus it is used the other video compression standards that come after it. It was developed in 1988 but adopted later in the year 1990 as a video coding standard by the International Communication Union- Telecommunication Standardization sector (ITU-T). According to Ze-Nian and Mark (2004), H.261 was developed mainly for videoconferencing, videophone and other audiovisual services over ISDN telephone lines. Although intended to support multiples of 384 Kbps from 1 to 5 channels, it ended up supporting rates of p * 64 Kbps where p ranged from 1 to 30. According to Wang et al. (2002) H.261 supports CIF (Common Intermediate Format), a videoconferencing format specifying 30fps (frames per second) video containing 288 lines and 352 pixels per line, and QCIF (Quarter Common Intermediate Format), a videoconferencing format that specifies data rates of 30 frames per second (fps), with each frame containing 144 lines and 176 pixels per line. H.263 This video coding standard is an improvement of the H.261 and it is used for video conferencing and other audiovisual services over the public service telephone network. In other words, it was developed for the internet videoconferencing applications. It was adopted by the International Communication Union- Telecommunication Standardization sector (ITU-T) in 1995. Ze-Nian and Mark (2004) advocates that it uses predictive coding for inter-frames which reduces temporal redundancy and reduce spatial redundancy by using transform coding for the remaining signals under compression. H.263 uses both CIF and QCIF and on top of that it uses sub-QCIF, 4CIF and 16CIF. MPEG-1 Moving Pictures Expert Group (MPEG) is a group that was formed in 1988 and its main task was to create a standard for delivery of video and audio. The International Organization for Standardization\ International Electrotechnical Commission (ISO/IEC) approved MPEG-1 audio/video coding standard for coding moving pictures and associated audio for digital storage media at up to 1.5 Mbits/s. (International Standard: ISO/IEC 11172, 1995) This common storage media may be CDs or VCDs coded at a rate of 1.5 Mps while coded video uses 1.2 Mbps and stereo audio uses 256 Kbps.MPEG adopts the Source input Format (SIF) which is basically the CCIR601 Digital TV format. MPEG-1 picture resolution is 352 * 240 for NTSC Video at 30 fps, or 352 * 288 for PAL video at 25 fps. It uses 4:2:0 chroma sub-sampling, as suggested by Ze-Nian and Mark (2004). MPEG-2 This video coding standard was approved by the ISO/IEC Moving Pictures Expert Group in 1994. MPEG-2 was developed for high quality video at a bitrates of more than 4 Mbps. It was then adopted for High Definition Television (HDTV). In addition to that it has been accepted for transmission over cable, satellite or terrestrial networks. It has also been adopted for digital versatile discs DVDs. Haskell et al. (1997) gives the result of a study made, MPEG-2 supports interlaced video where each frame consists of two fields, referred to as top field and bottom field. It defined seven profiles aimed at different applications which are Main, Simple, SNR scalable, Spatially Scalable, High, 4:2:2, and Multi-view. Within each profile, up to four levels are defined. For Instance High Level supports a high picture resolution of 1,920 x 1,152, a maximum frame rate of 60 fps. The maximum pixel rate of 62.7 x 106 per second, and a maximum data rate after coding of 80 Mbps. Differences of the Video coding standards With the video standards discussed above, we can now cite the differences between them. A tabulated result of these results will be appropriate to show the difference in characteristics. For this, one should consider the following factors: raw data rate, compressed data rate, application used, and the video format. Standards Video Format Raw Data Rate Compressed Data Rate Application H.261 CIF 37 Mbps >=384 Kbps Video conferencing over ISDN QCIF 9.1 Mbps >=64 Kbps H.263 4CIF/ CIF/ QCIF >=64 Kbps Video conferencing over Internet MPEG-1 CIF 30 Mbps 1.5 Mbps Video distribution on CD/ WWW MPEG-2 CCIR601 4:2:0 128 Mbps 3-10 Mbps Video distribution on DVD / digital TV Table 1: Difference in Video Coding Standards The table above shows the differences between H.261, H.263, MPEG-1, and MPEG-2 video coding standards based on a few of their characteristic. As mentioned at the beginning of the discussion, these standards are used for different applications and some standards may not exactly fit an application it is not meant for. Conclusion We have discussed some of the Video Coding Standards including H.261, H.263, MPEG-1, and MPEG-2 and tried to outline their characteristics and with that evident differences have been seen. These standards were developed by different group including the International Communication Union- Telecommunication Standardization sector (ITU-T), The International Organization for Standardization\ International Electrotechnical Commission (ISO/IEC) and Moving Pictures Expert Group (MPEG). The standardization was necessary so that application developers would develop applications that can work on several platforms. The standards discussed above show a progressive nature of video coding standards and this is due to the changing technology. Newer and better methods of transmitting and processing data have come up allowing better compression rates to be achieved. Some video coding standards that came after the standards discussed above include MPEG-4, GA-HDTV, and MPEG-7. They include better attributes to suit current applications. References Chen, J., Ut-Va Koc, & Ray Liu ,K. J. ( 2002) Design of Digital Video Coding Systems: a Complete Compressed Domain Approach. New York: Marcel Dekker Common Intermediate Format | Define Common Intermediate ... (n.d.). Retrieved from http://dictionary.reference.com/browse/Common%20Intermediate%20Format Fundamentals of Multimedia, Ze-Nian and Mark Li and Mark S. Drew (2004), ISBN: 0130618721, Prentice-Hall Haskell, B. G., Puri A., & Netravali, A. (1997) Digital Video: An Introduction to MPEG-2 New York: ChapMan & Hall. Information Technology – Coding of Moving Pictures and Associated Audio for Digital Storage media at up to about 1.5 Mbits/s (1992). International Standards:ISO/IEC 11172. Wang Y., Ostermann J., & Zhang Y. Q. (2002). Video Processing and Communications, Upper Saddle River, NJ: Prentice Hall. Read More