Digital subchannel
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Digital television in the United States supports multiple digital subchannels if you divide the 19.4 Megabits-per-second (Mbit/s) bitstream. Full quality 1080i HDTV requires 18 Mbit/s; however, many stations compress this down to 11 Mbit/s. A 720p HDTV signal can be compressed to 8 Mbit/s, and a SD signal compressed to 6 Mbit/s without perceivable loss of quality. 4 Mbit/s or less yields acceptable results if the subject in the video moves very little (such as a slideshow automated weather channel).
Therefore, station managers could run any of the following scenarios:
| Scenario | Picture Format |
|---|---|
| Scenario A | 1 slightly compressed 1080i HDTV |
| Scenario B | 1 Compressed 1080i HDTV + 1 x Compressed 720p HDTV Subchannel |
| Scenario C | 1 Compressed 1080i HDTV + 1 x Compressed SD Subchannel + Optional Slideshow type subchannel (such as NBC Weather Plus) |
| Scenario D | 3 Compressed SD Channels |
| Scenario E | 4 Highly Compressed SD Channels |
Many PBS stations around the country broadcast 4 SD channels during the daytime, and 1 HD + 1 SD channel at night. PBS offers the following channels: PBS DT, PBS HD, PBS Kids & Family, PBS Select, & PBS Learner.
With the launches of The CW and MyNetworkTV, many television stations have been launching subchannels affiliating with The CW or MyNetworkTV. Other stations have launched separate independent stations on their DT-2 signals, such as WOWT and WDJT (which carries its broadcast Class A station WMLW as a digital signal).
[edit] See also
- In-band on-channel (IBOC), digital radio technology allowing digital subchannels on FM stations
- The CW Plus
- NBC Weather Plus
- The Tube (TV channel)
