Transcript Multimedia Elements Sound, Animation, and Video

Multimedia Elements
Sound, Animation, and
Video
Sound
Analog wave patterns – these wave
patterns have two attributes
Volume – the height of each peak in the sound
wave
Frequency – (sometimes referred to as pitch)
the distance between the peaks. The greater
the distance, the lower the sound.
Image: scanned from Multimedia Concepts – James Schuman
Sampling
To include sound in a multimedia
application, the sound waves must be
converted from analog to digital form
This conversion is called sampling – every
fraction of a second a sample the of sound
is recorded in digital bits
Sampling
 Two factors affect the quality of digitized
sound
1) Sample rate – the number of times the sample
is taken
 Most common sampling rates are: 11.025, 22.05,
and 44.1 kHz
2) Sample size – the amount of information
stored about the sample
 Most common sampling sizes are: 8 and 16 bit
Sampling
Image: scanned from Multimedia Concepts – James Schuman
Sound File Formats
WAV format – filename.wav
AIFF (Audio Interchange File Format)
AIFFC (compressed)
RealAudio – filename.ra
MP3 (mpeg layer 3)
Sound on the Internet
Your first consideration when using sound
on the Internet is file size
Uncompressed files can be very large
A 10 second recording of an audio CD can be
as large as 2MB
Sound Tips for the Internet
Appropriate
Use
Consider the appropriateness of using sound. Some
sounds are content-related, such as hearing a foreign
phrase pronounced. Other sounds are for effect, such
as creating a mood or setting a scene. Avoid using
sound when there is no compelling benefit.
Quality
Start with the highest-quality sound available and
reduce the file size by converting the audio file to a
compressed format. When possible, avoid using free
sound clips available from the Internet. These are often
of poor quality and overused.
Cost
When recording audio files, it may be cost-prohibitive to
considerations contract with a recording studio and hire professional
talent. Investing in reasonably high-end equipment
(such as a sound card, microphone, and recording and
editing software), however, will prove worthwhile.
Sound Tips for the Internet
Alternative Consider using sound and still images as an alternative to
Methods
video to reduce file sizes. It may be just as effective to
show a photograph of a speaker and play the sound file of
the speech as it is to show a video of a “talking head.”
Streaming
Consider streaming the audio, especially for large files.
User
Control
If appropriate, provide a way to give the user some
control over the audio. Consider allowing the user to skip
a sound clip or adjust the volume. This issue is especially
important if a musical introduction is played when the user
first enters a Web site. The second time visiting the site,
the user may not want to hear the musical introduction.
Animation on the Internet
Animation is an excellent way to provide
appeal on a web site, choose from the
following
Animated text
Animated GIF’s
Marcomedia Director applications
3-D environments
2-D Animation
Two types of animation exist
Cel animation – based on changes that occur
form one frame to the next
Path animation – moves an object along a
predetermined path on the screen
3-D Animation
 3-D Animation involves three steps
1) Modeling – creating the broad contours and
structure of 3-D objects and scenes
2) Animation – defining the object’s motion
3) Rendering – giving objects attributes such as
color, surface textures, and amounts of
transparency
3-D Animation
Image: scanned from Multimedia Concepts – James Schuman
3-D Animation Special Effects
Morphing – blending together two images
into a series of images
Warping – distorts a single image
Virtual Reality – creates an environment
that surrounds the user so that he or she
becomes part of the experience
Animation
Animated text – using the HTML <blink>
command causes text to flash on and off
Animated gif – using a software program
to create a series of gif files such as GIF
Builder
Director movie – animation played using
Shockwave plug-in
3-D environments – a computer language
used to create 3-D images
Design Considerations
Give the user control over whether or not
to display or enlarge graphic images
Allow the user to be active while graphic
images are being displayed
Provide feedback to the user by displaying
the amount of time a file will take to
download
Video
Video, like sound, is recorded and played
an as analog signal
Analog video must be digitized in order for
it to put into a multimedia file
Digital video has many advantages, but
file size is important
Video
Several elements determine file size:
Frame rate
Image size
Color depth
To determine file size use the following
formula:
Frames per second X image size X color depth
/ 8 = file size
Video Compression and Editing
There are two types of video compression
Lossless – preserves the exact image
throughout the compression
Lossy – eliminates some of the data in the
image (provides greater compression ratios
than lossless)
Remember – there is always a trade off, file
size versus image quality
Video on the Internet
There are two types of video transfer over
the Internet
HTTP (Hypertext Transfer Protocol) –
downloads the entire video to the hard drive on
the user’s computer
RTSP (Real-Time Streaming Protocol) – is a
continuous-playing, streaming technology in
which the user’s computer is in constant contact
with the server playing the video
Video Tips
Color
depth
Reducing the color depth to less than 256 colors
gives a markedly poorer-quality image.
Frame
rate
Reducing the frame rate to less than 15 frames
per second causes a noticeable and distracting
jerkiness that is usually unacceptable.
File size A technique for reducing file size is to minimize
the use of video in the image that appears on
the screen – that is, to create video only for the
parts of an object that are changing, such as a
flickering candle. The video could be played over
and over to create the motion of a flickering
candle.
Video Tips
Display size
In most multimedia titles, you do not need
to show full-screen video. The video can
be played in a window that can be as
small as one-fourth or even one-sixteenth
the size of the screen.
Conclusion: Changing the image size and compressing
the file become the primary ways of reducing file size. In
most cases, a one-quarter screen image (320 X 240), an 8bit (256 colors) color depth, and a 15 frames per second
frame rate are acceptable in a multimedia title.
The End
University of North Texas
Dr. Vicky Cereijo