H.261

H.261 is a video compression standard developed by the International Telecommunication Union (ITU) in collaboration with experts from Bell Labs, IBM, and Microsoft. The standard was designed to facilitate video conferencing and other video transmission applications over Integrated Services Digital Network (ISDN) lines, which were widely used at the time by AT&T, British Telecom, and Deutsche Telekom. The development of H.261 was influenced by earlier video compression standards, such as H.120, and was later succeeded by more advanced standards like H.262 and H.263, which were used in applications like VideoCD and DVD. The work on H.261 was also related to the development of other standards, such as MPEG-1, by organizations like the Moving Picture Experts Group (MPEG) and the Society of Motion Picture and Television Engineers (SMPTE).

Introduction

H.261 is a lossy video compression standard that uses a combination of Discrete Cosine Transform (DCT) and Quantization to reduce the amount of data required to represent a video signal. The standard was designed to operate at bitrates between 40 and 1920 kbit/s, making it suitable for use over ISDN lines, which were commonly used by Cisco Systems, Juniper Networks, and Alcatel-Lucent. H.261 was also used in various video conferencing systems, including those developed by Polycom, Cisco Systems, and Microsoft, and was supported by Intel and AMD processors. The standard's development was influenced by the work of researchers at MIT, Stanford University, and University of California, Berkeley, and was later used in applications like Telepresence and Video streaming by companies like Google, Amazon, and Facebook.

History

The development of H.261 began in the late 1980s, with the first version of the standard being published in 1988 by the International Telecommunication Union (ITU). The standard was developed in collaboration with experts from Bell Labs, IBM, and Microsoft, and was influenced by earlier video compression standards, such as H.120, which was used in applications like Video conferencing and Remote desktop. The development of H.261 was also related to the work of researchers at MIT, Stanford University, and University of California, Berkeley, who were working on other video compression standards, such as MPEG-1, which was used in applications like VideoCD and DVD. The standard was later updated in 1993 to include support for additional features, such as Error correction and Error concealment, which were used in applications like Satellite television and Cable television by companies like DirecTV, Dish Network, and Comcast.

Technical Details

H.261 uses a combination of Discrete Cosine Transform (DCT) and Quantization to reduce the amount of data required to represent a video signal. The standard supports two types of video frames: Intra-frames (I-frames) and Inter-frames (P-frames), which are used in applications like Video editing and Video streaming by companies like Adobe Systems, Avid Technology, and Apple Inc.. I-frames are used to represent a complete video frame, while P-frames are used to represent the difference between two consecutive video frames, which is used in applications like Video conferencing and Remote desktop by companies like Polycom, Cisco Systems, and Microsoft. The standard also supports a variety of Chroma subsampling schemes, including 4:2:0 and 4:2:2, which are used in applications like High-definition television (HDTV) and Ultra-high-definition television (UHDTV) by companies like Sony, Samsung, and LG Electronics.

Applications

H.261 was widely used in various video conferencing systems, including those developed by Polycom, Cisco Systems, and Microsoft, and was supported by Intel and AMD processors. The standard was also used in other applications, such as Video streaming and Telepresence, by companies like Google, Amazon, and Facebook. H.261 was also used in various Set-top boxes and Digital video recorders (DVRs), which were developed by companies like TiVo, ReplayTV, and Dish Network, and was supported by Cable television and Satellite television providers like Comcast, DirecTV, and Dish Network. The standard's use in these applications was influenced by the work of researchers at MIT, Stanford University, and University of California, Berkeley, and was later replaced by more advanced standards like H.262 and H.263, which were used in applications like VideoCD and DVD.

Legacy and Impact

H.261 played an important role in the development of video compression standards, and its influence can be seen in later standards like H.262 and H.263, which were used in applications like VideoCD and DVD. The standard's use of Discrete Cosine Transform (DCT) and Quantization has become a widely accepted approach to video compression, and is used in many modern video compression standards, including H.264 and H.265, which are used in applications like Blu-ray Disc and Ultra-high-definition television (UHDTV) by companies like Sony, Samsung, and LG Electronics. H.261 also played a key role in the development of video conferencing and Telepresence technologies, which are now widely used by companies like Google, Amazon, and Facebook, and was supported by Intel and AMD processors. The standard's legacy can be seen in the work of researchers at MIT, Stanford University, and University of California, Berkeley, who continue to develop new video compression standards and technologies, such as VP9 and AV1, which are used in applications like YouTube and Netflix by companies like Google and Netflix. Category:Video codecs