Why does digital cable tv have about a five second delay compared to an antenna based transmission?

Answer 1

Analog television services are the traditional format for television broadcast. Antenna based or terrestrial broadcasts have used analog signals since the advent of television. In most analog transmissions, the signal is delivered as it is created. The signal may well pass through a long chain of equipment from the camera to the transmitter and then to a television but the signal is not stored at any point. The picture is seen virtually at the same time as it was created.

Digital transmission (Cable, satellite and digital terrestrial) don't have the same restriction. Before the signal is broadcast it is compressed to reduce the amount of bandwidth required. The compression process can add a second or two. When the digital television receiver decodes the signal to its uncompressed form, that too will add a second or more.

Finally, signals are routed through a variety of connections from the studio to transmission control centers and then to the transmitters. The signal is divided into packets of a few frames. As with the internet, some of these packets can be delayed and arrive later than the other packets around them. By storing the packets for a small amount of time, delayed packets are given the chance to catch up. This adds another delay to the image.

The end result is that the digital signal will always be later than the analog equivalent. As long as we see a complete television program, we are none the wiser. It is only when we watch the same program on analog and digital services at the same time do we realize that there is a delay. Although the delay is of no consequence, it does mean that we now see nothing that is truly live. It's worth remembering that when you see a touch down at the next "live" broadcast of the Superbowl , it's already history!