Multimedia ElementsSound, 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.wavAIFF (Audio Interchange File Format)AIFFC (compressed)RealAudio – filename.raMP3 (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 InternetAppropriate 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 considerations

When recording audio files, it may be cost-prohibitive to 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 Methods

Consider using sound and still images as an alternative to 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 steps1) 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 8-bit (256 colors) color depth, and a 15 frames per second frame rate are acceptable in a multimedia title.

The EndUniversity of North Texas

Dr. Vicky Cereijo