Definition: set-top box

A device that converts video content to earlier analog or today's digital TV signals. For years, the set-top box (STB) was the cable box that "sat on top" of the TV because there was ample room. Cable TV providers give customers their own set-top boxes; however, anyone can purchase an Apple TV or Roku hub that connects to the home network for Internet access and streaming services such as Netflix and Hulu. These "media hubs" go by many names and may accept local content from the home network as well (see digital media hub).

Receivers and Converters
A satellite TV set-top box is officially a "satellite receiver," and the box that converts over-the-air digital broadcasts to analog for old TVs is a "converter" (see TV converter box).

The Cable Set-Top Box
In the days of analog TV, cable boxes descrambled premium channels and managed the high channel numbers early TVs did not support. They were generally one-way communications. For today's bidirectional digital service, the cable box decodes MPEG video frames, decrypts the premium channels and stores and displays the program guides. Also providing upstream transmission for content selection, cable boxes may have a built-in DVR for recording onto a storage drive. See DVR.

Many cable TV companies also offer Internet service, but their set-top boxes are only for TV. The cable coming into the house is split into two lines: one to the set-top box and the other to the cable modem for Internet access. See MPEG, CableCARD, cable modem and hybrid set-top box.

Set It On Top

For decades, people placed cable boxes on top of their CRT or projection TV sets because the units had plenty of depth (bottom). Although TVs no longer have a flat surface to rest anything, the term lives on as in this Xfinity TV cable message when rewind on the remote is pressed (top).

Big and Little

The Motorola unit (top) connects to the cable company's coaxial cable, whereas the Apple TV (only four inches wide) gets its content via Ethernet or Wi-Fi.

Not as Elegant as the Sales Brochure

In practice, today's streaming set-top boxes are often hidden in the A/V cabinet and nothing much to look at. These three plug into the A/V receiver via HDMI and connect to the home network via the Ethernet switch.

Legacy Support in a Set-top Box

Older set-top boxes such as this Roku unit had analog outputs to accommodate legacy TVs. However, HDMI has pretty much replaced this variety of connectivity (see HDMI).