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 Sample rate – the number of times the sample is taken Most common sampling rates are: 11.025, 22.05, and 44.1 kHz 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 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 steps Modeling – creating the broad contours and structure of 3-D objects and scenes Animation – defining the object’s motion 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.

University of North Texas Dr. Vicky Cereijo The End University of North Texas Dr. Vicky Cereijo