Definition: set-top box

A device that converts video content to analog or digital TV signals. For years, the set-top box (STB) was the cable box that "sat on top" of the TV. Although no more flat surface to rest anything, the term lives on.

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).

Apple TV, Fire TV, Android TV and Roku boxes connect to the home network for Internet access and convert video from Netflix, Hulu and other providers into TV signals. These "media hubs" go by many names and may accept local content from the home network as well (see digital media hub).

The Cable Set-Top Box
In the days of analog TV, cable boxes descrambled the premium channels and managed the high channel numbers very early TVs did not support. For today's digital service, the cable box decodes MPEG video frames, decrypts the premium channels and stores and displays the program guides. Also providing upstream communications for video-on-demand, digital cable boxes often have a built-in DVR for recording content on a hard drive.

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, DVR, CableCARD, cable modem and hybrid set-top box.

Set It On Top

For years, people placed cable boxes on top of their CRT or projection TV sets because there was plenty of room.

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).