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Module 47 |
Updated: 04/15/2011 |
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Consumer Video Formatsand Video Compression
In this module we will cover:
Although this may be one of the prices we have to pay for progress, it has also added confusion to video production. In this discussion we'll skip over most of the video formats that have been introduced over the years -- most of them didn't stay around too long anyway -- and very briefly look at what have been the most widely used. In this module we'll focus on consumer videotape equipment. In the next module we'll cover professional equipment -- although, in recent years the dividing line between these categories has gotten a bit blurred. Serious hobbyists often select professional equipment, and consumer equipment often finds its way into professional applications. Before we start our discussion of consumer
formats we need to go into something that we've previously mentioned but not really explained: data or digital compression. Digital CompressionLossy and Lossless Compression
With lossless compression there is no difference -- or some people would say, no readily discernible difference -- between the original and the compressed data. Thus, no loss in quality. The problem, however, is that lossless techniques involve huge amounts of data and are technically quite demanding. Thus, they require expensive equipment. Most video and audio compression techniques eliminate
data to some degree to make recording and transmission technically
easier. It then becomes a matter of how much the
data is compressed. When to the trained eye quality starts to be sacrificed,
the term lossy compression is used. Compression Ratios You can easily use a 2:1 compression with video without noticing any loss in quality. In fact, you can even compress video to 10:1 without noticing a significant difference -- and, in the process, of course, you can record the data in 1/10 the space. When you move to 20:1 (depending on the subject matter), you will still have an excellent picture, even though a trained eye will notice a slight loss in quality. Using the right compression techniques, compression ratios today go as high as 100:1. Note in the windows and in the face in the photo on the right below the subtle pattern added by compression. Compare that with the photo on the left that has minimal compression. The enlargements from these images (below these photos) make the differences much more obvious.
This difference is much more noticeable in the 300% enlargements in the two photos on the left below.
As you move to 50:1 and beyond, you can begin to see a noticeable (and objectionable) difference between the original picture and the compressed version. In full motion compressed video you often see discrete data blocks or rectangles in the video, especially during rapid action involving large areas of the picture. Note photo on the right above.
Compression Codecs Top-of-the-line digital camcorders use so-called "no compromise"
digital 4:2:2 compression. Explaining these
numbers would get us into some deep technical waters, so
just keep in mind that 4:4:4 is a pure, uncompromised (uncompressed) signal;
4:2:2 represents minimal and unnoticed compression; and 4:1:1, which is associated
with consumer camcorders, involves significant signal compression. MPEG-2 and MPEG-4 Compression
However, rapidly changing subject matter such as a hockey game is particularly taxing for a compression scheme. In this case
the discarded data may be necessary to reproduce all of the detail
in the action. It is in this type of subject matter that you are most
apt to see artifacts, visible video aberrations or problems caused by the compression
scheme not keeping up with the speed of action.
An Uncompromised Future? However, as data storage becomes cheaper and more compact and computer chips become faster, uncompressed or minimally compressed audio and video may become the norm -- at least in the initial stages of video production. This will significantly improve the quality of productions -- especially HDTV productions -- that go through numerous stages of editing.
Consumer Video Formats
Betamax was finally discontinued in 2002. |
VHS The VHS format lasted more than 20 years
and spawned hundreds of thousands of video rental stores around
the world. However, as you can see form the graph below, things quickly By 2008, most movie rental stores had relegated VHS tapes to a small section in the back of the store, and by 2009, VHS tapes were no longer being produced.
This format, which we'll discuss in more detail later, offers more than five times the storage capacity of traditional DVDs. Blu-ray is a high-definition video format that's backwards compatible with CDs and DVDs.
This minimized any subsequent loss in quality due to
editing. For a discussion of acquisition
formats
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Seeing something is quite different from reading about it. Although an event may take place that can and should elicit a public outcry of opposition, until it is recorded on video for "all the world to see," little may be done. (A striking example is the story of Neda that we've mentioned before.
We
don't showcase videos on this site, primarily because of sites such as YouTube
can do a better job.
Here are just a few of the
other options available.
Compared
to film, digital video has its own unique characteristics. It can
look sharper and colder than film, and exhibit compression artifacts
that many people feel detract from the video medium.
At the same time, for those who feel these things are
not desirable, there are a variety of filters available that can counteract
these effects. These are discussed
here.
*
David Pogue, probably the best known technical writer today, suggests that it
wasn't the cell phone that killed the Flip, but
the need of Cisco (the company who bought out the Flip) to use bits of the
superior technology in other products. Seven million of these camcorders
were sold, representing a record-setting 35 percent of the camcorder
market. The Flip line was canceled within a day of the introduction of a new
model that would have made possible live Internet broadcasts.
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