MythTV provides functionality similar to a TiVo or Replay device. However, as an Open Source project it offers many additional features and allows you to make modifications yourself.
Besides the standard digital video recorder (DVR) functions, such as recording and playing back programs and schedule recordings, a number of plugins are available that enable the user to play external video, listen to music, view photos, browse the web, get weather information, use a TV and a web camera as a videophone over the Internet, etc.
You can simultaneously record as many programs as you have TV tuners. Capture cards typically contain one TV tuner, but some cards include more than one tuner. Watching live TV will occupy one tuner that will not be available for recording at that time. If you want to watch high definition broadcasts, you need a capture card with that capability.
Channels can be received either over the air using an antenna or through cable from your cable TV provider. One way to find out what channels are available in your area is to go to labs.zap2it.com and type in your zip code in the search box. You can recognize digital TV channels by the "DT" suffix and high definition channels by an "HD".
Recording TV programs can require a lot of storage space, as you can image. Depending on the resolution and compression schemes, one hour of recording can occupy 3-5 GB of your hard disk. For more information see here.
