standarddefinition

Standard-definition (SD) is a term used to describe a class of video resolution and quality that predates and contrasts with high-definition (HD) video. SD encompasses both traditional analog television systems and subsequent digital formats that deliver lower resolution images. In analog broadcasting, SD is associated with two main families: NTSC, used in North America and parts of Asia, with about 525 lines per frame, and PAL and SECAM, used in much of Europe, Africa, and parts of Asia, with about 625 lines per frame. In digital video, SD typically refers to non-high-definition content such as 480i/576i, and common display resolutions of 720x480 (NTSC regions) or 720x576 (PAL/SECAM regions). These formats are usually displayed with 4:3 aspect ratio, or 16:9 when anamorphic storage or letterboxing is used.

SD was the standard baseline for television production and distribution from the mid-20th century until the shift to HD in the 2000s and 2010s. It remains widespread for legacy broadcasts, DVDs, and many streaming services that adjust quality to bandwidth. The term is sometimes extended to refer to any video not transmitted in HD, including some compressed streaming at standard-definition bitrates.

Examples and variants include computer-oriented resolutions such as 640x480 (VGA) and 720x480 in some video capture contexts. Formats like 480i, 576i, and their progressive counterparts (480p, 576p) are used in various devices and media. In practice, SD is often contrasted with HD, which begins at 720p or 1080i/p. The transition to HD continues, but SD remains relevant for archived content and lower-bandwidth applications.