Image Processing Reference
7 of those 8 frames, but that task was likely delegated to a graphics co-processor anyway.
Your CPU is still going to be working quite hard.
The trick-play features inform the way that you set up the encoding. You might, for
example, place I-frames at useful intervals and shorten the GOP length in order to
improve the fast-forward playback quality.
This is implemented in a very simple way. It is only necessary to discard every other
frame. The computational effort involved depends on whether it is necessary to decode
only a single I-frame or several P- and B-frames to extract the required image. Encoded
video should be played forward; later versions of the standards allow for bi-directional
playback, so reverse play is also supported as a trivial engineering task.
Implementing this is easy because you simply stop the decoder. Pausing digital TV ser-
vices presents a very stable and high-quality paused picture when compared with the per-
formance of a VHS player. If you recall the kind of artifacts that analog suffered from when
being paused, you will see that even gross digital artifacts yield a still image of superior
Already, companies are starting to investigate delivering DVR technology, which will cope
with HDTV services. Pace is a company that makes set-top boxes that other companies can
then brand with their own logo and add value to. They have introduced an HD-capable
DVR product for cable and satellite broadcasting.
Receiving TV on Your PC
Increasing numbers of hardware suppliers are packaging TV tuners in a way that is con-
venient for attachment to your PC. This enables you to display the broadcast TV in a win-
dow on the desktop or perhaps think about building your own media center and DVR
Alchemy TV, Hauppauge, and ElGato are three companies whose products are par-
ticularly successful. ElGato is an interesting case because it is attached by FireWire to a
Macintosh. This suggests that you could connect it to a laptop and receive digital TV in a
mobile situation. This is practical for DTT or might lend itself to DVB-H compatible
mobile services. Obviously DCable and DSat are non-starters in mobile situations because
of the dish size required or the permanent connection to a cable.
ElGato also offers receivers for DTV services as well as analog, and you can con-
nect to just about any kind of TV service you want. Some of their products are also