Digital Television and HDTV

Digital television transmits picture and sound as digital data rather than as the continuously varying analogue signals used by older systems. Encoding the signal digitally allows more channels to fit in the same bandwidth, supports widescreen and high-definition pictures, and makes the signal more robust against noise and interference. High-definition television (HDTV) is the part of digital television that offers much greater picture detail than the earlier standard-definition broadcasts, using many more lines and pixels per frame.

Sending full-resolution video would require an enormous amount of data, so digital television relies on compression. The MPEG family of standards, developed by the Moving Picture Experts Group, defines how this is done. MPEG-2 was widely adopted for digital broadcasting and for DVD video, while the later MPEG-4 family, including the widely used H.264 coding, achieves higher compression and is used for high-definition broadcasting, internet video and streaming. These schemes reduce data by removing redundancy within each frame and between successive frames, since much of a moving picture changes little from one frame to the next.

Different regions adopted different broadcasting standards for transmitting the compressed digital streams over the air, by cable and by satellite, each specifying how the data is modulated and carried. Together, digital encoding, MPEG compression and these transmission standards replaced analogue television in most countries, enabling more channels, higher picture quality and additional services such as electronic programme guides.

Frequently asked questions

Why does digital television need compression?

Uncompressed video contains far too much data to transmit efficiently. MPEG compression removes redundancy within and between frames so the signal fits the available bandwidth.

What is the difference between MPEG-2 and MPEG-4?

MPEG-2 was used for early digital broadcasts and DVDs, while the later MPEG-4 family, including H.264, compresses more efficiently and suits high-definition and internet video.

What makes HDTV different from standard television?

HDTV uses many more lines and pixels per frame, giving a sharper, more detailed picture, and is usually broadcast in a widescreen format.