Image Processing Reference
In-Depth Information
17
Tape Formats
17.1
Carry-On Luggage
Staying with our traveling analogy for a while longer, you don't just put things in a suit-
case when you're packing for a trip. You also use a carry-on bag in order to have some
things you'll need for the trip ready at hand. Similarly, files are fine for some types of stor-
age, but they aren't the only solution. Video gets stored on a variety of removable-media
formats—tapes, disks, memory sticks. Video is sometimes stored in these different media
as files, but more often it is recorded as something more like a broadcast bit stream.
17.2
Input Video Quality
Some of your video may be of questionable picture quality. For example, pictures taken on
mobile Webcams in remote news-gathering operations, perhaps in a war zone, may be very
noisy. This is improving as the codecs for transmission back to base improve. Bear in mind
that the best you will accomplish will be no better than that delivered by the remote source.
Selecting the wrong coding parameters might actually produce artifacts in the coded out-
put that are far worse because they are affected by artifacts in the incoming signal.
17.3
Grabbing an Analog Feed
A broadcast off-air signal encoded directly as an analog source might yield better results
than recording to VHS as an intermediate step. Beware when recording off-air material
though, as any material delivered via the digital TV services will have already been com-
pressed to MPEG-2 format, and the bit-rate ceilings may already have compromised the
quality at times. In that case, capturing the raw MPEG-2 stream is a better solution.
Even if you are encoding from an analog source these days, the origination and rout-
ing of the signals within the broadcasting infrastructure will occur via digital systems. If
any compression were applied along the way, this might interact with your compression
settings. It is important to understand the fundamental principle that you cannot get back
any information that has already been discarded by a compression process. You may
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