 | This article needs additional citations for verification. (May 2023) |
| Video codec for audiovisual services at p x 64 kbit/s | |
| Status | Published |
|---|---|
| Year started | 1988 |
| Latest version | (03/93) |
| Organization | ITU-T, Hitachi, PictureTel, NTT, BT, Toshiba, etc. |
| Committee | ITU-T Study Group 16 VCEG (then: Specialists Group on Coding for Visual Telephony) |
| Related standards | H.262, H.263, H.264, H.265, H.266, H.320, ISO/IEC 14496-2 |
| Domain | video compression |
| Website | https://www.itu.int/rec/T-REC-H.261 |
H.261 is an ITU-T video compression standard, first ratified in November 1988.[1][2] 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.
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).
- ^ "(Nokia position paper) Web Architecture and Codec Considerations for Audio-Visual Services" (PDF).
H.261, which (in its first version) was ratified in November 1988.
- ^ ITU-T (1988). "H.261 : Video codec for audiovisual services at p x 384 kbit/s - Recommendation H.261 (11/88)". Retrieved 2010-10-21.