H.261

H.261 is an ITU-T video compression standard, first ratified in November 1988. It is the first member of the H.26x family of video coding standards in the domain of the ITU-T Study Group 16 Video Coding Experts Group (VCEG, then Specialists Group on Coding for Visual Telephony). It was the first video coding standard that was useful in practical terms.

Key facts

Technology standard.title: H.261
Technology standard.long_name: Video codec for audiovisual services at p x 64 kbit/s
Technology standard.status: Published
Technology standard.year_started: 1988
Technology standard.version: (03/93)
Technology standard.organization: ITU-T, Hitachi, PictureTel, NTT, BT, Toshiba, etc.
Technology standard.committee: ITU-T Study Group 16 VCEG (then: Specialists Group on Coding for Visual Telephony)
Technology standard.related_standards: H.262, H.263, H.264, H.265, H.266, H.320, ISO/IEC 14496-2
Technology standard.successor: H.262
Technology standard.domain: video compression
Technology standard.website: https://www.itu.int/rec/T-REC-H.261

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Wikidata facts

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publication date: 1988-00-00
media type: video/H261
file extension: h261

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Article

7 sections

Contents

History
H.261 design
Software implementations
Patent holders
See also
References
External links

H.261 was originally designed for transmission over ISDN lines on which data rates are multiples of 64 kbit/s. The coding algorithm was designed to be able to operate at video bit rates between 40 kbit/s and 2 Mbit/s. The standard supports two video frame sizes: CIF (352×288 luma with 176×144 chroma) and QCIF (176×144 with 88×72 chroma) using a 4:2:0 sampling scheme. It also has a backward-compatible trick for sending still images with 704×576 luma resolution and 352×288 chroma resolution (which was added in a later revision in 1993).