Introduction to Media Production Video Basics Topics covered in this lecture Video Quality Frame Rate Less bandwidth Resolution Compression Codec How Video Cameras Work Digital Video and Videotape Standards Video Storage Media Streaming Media 1/47
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Introduction to Media Production
Video Basics
Topics covered in this lecture
Video Quality
Frame Rate
Less bandwidth Resolution
Compression
Codec
How Video Cameras Work
Digital Video and Videotape Standards
Video Storage Media
Streaming Media
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Video Quality
Video quality derives from three factors:
Frame rate, Resolution, and Compression.
As the frame rate and resolution increase and the compression decreases, quality rises dramatically.
However, it does so at a cost: bandwidth and storage.
Bandwidth (also known as bit rate)
Bandwidth refers to the amount of data that a system can push through some communications device
at any time, e.g. bit/second. As the bandwidth of the Internet is limited, the bigger the bandwidth the
video requests, the slower download time.
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IEEE-1394 (FireWire or I-LINK) offers another demonstration of bandwidth efficiency. It allows
you to transfer high-quality video in real time from your camera to your computer. The USB ports
also allow near-1394 efficiency because they offer higher bandwidth capacity.
Storage refers to the total space used to store your video. A small, highly compressed, low-frame-
rate video might take up a few megabytes. In contrast, a longer, better-quality, high-frame-rate
feature might occupy literally tens or hundreds of gigabytes.
The better the video, the higher the bandwidth and storage demands will be. You must balance
production values with your computer’s limitations.
Frame Rate
Many people have tried to explain the magic of movies and video. Some attribute it to a
physiological feature called persistence of vision. In persistence of vision, our eyes and brain try to
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hold onto a series of sequential images, forming the illusion of motion. Others point to more general
cognitive functions that allow us to integrate and interpolate movement.
When we’re shown a series of pictures at a certain rate, they begin to fuse together into an illusion of
smooth movement. This rate is called the critical fusion frequency (CFF) which refers to the rate at
which the screen needs to refresh in order to avoid flicker and allow the picture to appear steady to
the viewer.
As a rule of thumb, the higher the frame rate, the smoother the motion you’ll experience .
(1) At 10fps offers the absolute lowest frame rate that lets us perceive smooth motion.
Video that is slower than 10fps appears jerky with a strong jitter.
(2) At about 24fps to 30fps, video runs smoothly without perceptible roughness. Motion
pictures project film at 24fps. Most TV systems broadcast at approximately 30fps.
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Of course, as the frame rate increases, so will the total number of frames you’ll need to process and
store per second. More frames mean more disk space and, if you plan to broadcast over the Internet,
more bandwidth to transmit your video.
Figure 3.6: Higher frame rates require more bandwidth and
storage. Reducing the number of frames per second reduces
both storage and bandwidth requirements.
Less Bandwidth Resolution
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Resolution refers to the amount of picture detail in each video frame. The terms horizontal resolution
and vertical resolution refer to the number of pixels that lie, respectively, along the width and the
height of a frame.
As the resolution increases, you see more picture detail, so the image becomes clearer and easier to
view. Of course, as the resolution increases, so does the size of each frame, and that brings us back
to bandwidth and storage.
Large frames occupy a lot of bandwidth and storage space. If
you increase frame resolution by as little as 10 percent, you
end up increasing the size of your entire movie by 10 percent.
A 10 percent increase in frame resolution isn’t really much
improvement, but a 10 percent increase in movie size can be
huge.
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Compression
Compression allows you to store video data more efficiently by squeezing the picture down to a
manageable size. With compression, your video presents similar quality picture while using a
smaller amount of storage.
As the compression rates rise, storage requirements decrease. Pictures fit into a smaller space. While
this might seem like an ideal solution for both bandwidth and storage issues, you must take two key
compression factors into consideration: lossiness and decompression time. These factors greatly
affect the quality of the final video.
Lossiness refers to a quality decrease produced by the compression process . Lossiness means
that the picture you see when you decompress won’t be exactly the same picture you originally
compressed.
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Time is the other factor associated with compression. A compressed video needs to be restored
(decompressed) to be viewed. It takes time—often a lot of it—to decompress your video. If this is
done before watching the video, there’s no problem. However, if you need to watch the video at the
same time as you decompress it (watch it real time), decompression time makes a difference. Few
things are harder to watch than a video that keeps pausing to decompress the next segment. Anyone
who has attempted to watch a DVD on an old, slow computer with software decompression has had
this experience.
Standard digital video uses a 5:1 compression ratio.
Web Video might be compressed as much as 50:1 or even 100:1.
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Codec
Codec refer to a large variety of algorithms/computer programmes (e.g. that COmpress and
DECompress video and other types of images. There’s nothing magical or remarkable about codec.
They’re simply a number of standards that people have developed to optimize some playback feature
or another.
Some codec produce highly compressed, fast-playing videos. Others offer excellent motion
reproduction or good-quality stills. If we didn’t need to compress video, we wouldn’t need to use
codec at all. As it is, each codec serves a different purpose. The table below lists some of the more