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Introduction to Multimedia

SMM 2005Muhd. Nabil Ahmad Zawawi

Jabatan Multimedia, FSKTM, UPM

[email protected]://www.fsktm.upm.edu.my/~nabil/

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Introduction to Multimedia

Chapter 6

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6.1 Video Concept

Video is an excellent tool for delivering multimedia. Video places the highest performance demand on

computer and its memory and storage. Digital video has replaced analog video as the method

of choice for making and delivering video for multimedia.

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6.1 Video Concept

Digital video device produces excellent finished products at a fraction of the cost of analog.

Digital video eliminates the image-degrading analog-to-digital conversion.

Many digital video sources exist, but getting the rights can be difficult, time-consuming, and expensive.

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6.2 Analogue Video

Video information that is stored using television video signals, film, videotape or other non-computer media

Each frame is represented by a fluctuating voltage signal known as an analogue wave form or composite video.

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6.2 Analogue Video Composite analogue video has all the video

components: brightness, colour and synchronization

Then combined into one signal for delivery Example : traditional television Problems: colour blending, low clarity, high generation

lost, difficult to edit.

DIGITAL ANALOGUE

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Digitizing Video

Digital video combines features of graphics and audio to create dynamic content for multimedia products.

Video is simply moving pictures. Digitized video can be edited more easily. Digitized video files can be extremely large.

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Digitizing Video

Digital video is often used to capture content from movies and television to be used in multimedia.

A video source (video camera ,VCR, TV or videodisc) is connected to a video capture card in a computer.

As the video source is played, the analog signal is sent to the video card and converted into a digital file (including sound from the video).

VCRVCR

Video Overlay Board /Video Overlay Board /Video Capture CardVideo Capture Card

PCPC

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Analogue signal from VCRConverted to DIGITALby VIDEO CAPTURE CARD

The converted signal isentered inside a computer

Signal is processedVideo is edited using video editing software software

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6.3 Digital Video

Digital video is the digitisation of analogue video signals into numerical format

It creates the illusion of full motion by displaying a rapid sequence of changing images on a display device.

Conversion from analogue to digital format requires the use on an ADC (Analogue to Digital Converter)

A Digital to Analogue Converter (DAC) can be used to output digital video on analogue equipment

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6.3 Digital Video

Video clip stored on any mass-storage device can be played back on a computer’s monitor without special hardware.

Setting up a production environment for making digital video, requires some hardware specifications.

Some specifications include computer with FireWire connection and cables, fast processor, plenty of RAM, fast and big hard disk.

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File Size and Formats

There is an important consideration: file size in digitized video which included

1. frame rate

2. image size

3. color depth.

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1. Frame Rate animation is an illusion caused by the rapid

display of still images. television and movies play at 30 fps but

acceptable playback can be achieved with 15 fps.

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2. Image Size A standard full screen resolution is 640x480 pixels but to

safe storing space a video with 320x240 for a computer display is still acceptable.

New high-definition televisions (HDTV) are capable of resolutions up to 1920×1080p60, 1920 pixels per scan line by 1080 scan lines,

progressive, at 60 frames per second.

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3. Color Depth The quality of video is dependent on the color quality

(related to the number of colors) for each bitmap in the frame sequence.

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3. Color Depth The color depth below 256 colors is poorer-quality image. The frame rate to below 15 fps causes a noticeable and

distracting jerkiness that unacceptable. Changing the image size and compressing the file therefore

become primary ways of reducing file size.


24 bit 8 bit (256 colors)16 bit

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Video Editing Terminology

Linear It plays end to end in one direction, usually

pertains to videotape editing specifically the editing of linear tape segments into one final master tape.

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Video Editing Terminology

Non-linear Refers to the editing of disk-based digital video. The software provides an on screen map of what

the final video sequences should look like incorporating the edits, splices, special effects, transitions and sound tracks.

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Special Effects

Transitions Such as fading, wiping, splatters, scrolling, stipple and many

more are available by simply dragging and dropping that transition between the two video clips.

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Special Effects

Superimposing The ability to superimpose one clip over another is a valuable

technique. The technique of green screening is identical except that the

color green is used for the screen and later digitally removed. The blue screen and green screen superimposing are just two

of the superimposing technique available.

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Special Effects

Superimposing Digital video editing applications provide special effect filters

to create lens flares and emboss, tint, pan, twist and zoom the video image.

These special effects can often be set up to change over the duration of the video clip.

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6.4 Video Compression The video compression/decompression programs are used so that video can fit on a single

CD and the speed of transferring video from a CD to the computer can be increased. Let us say that a sequence of 25fps video is about 25MB. CD-ROM transfer rate is calculated as follows:

1X= 150KB per second 10X=1.5 MB per second 100X= 15 MB per secondt

To overcome large video size, CODECS were developed.

Compresses when saved

CODEC

File format used such as: Avi, Mpeg, Mov

Decompresses when needed

for display

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6.4 Video Compression

Digital video compression schemes or codecs is the algorithm used to compress (code) a video for delivery.

The codec then decodes the compressed video in real-time for fast playback.

Streaming audio and video starts playback as soon as enough data has transferred to the user’s computer to sustain this playback.

FULL VIDEO

Taken from the CD into memory buffer

DISPLAY ON SCREEN

MEMORY BUFFER

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Two types of COMPRESSION:Lossless compression.

Preserves the exact image throughout the compression and decompression process. E.g: text images is to identify repeating words and assign them a code.

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Two types of COMPRESSION:Lossy compression.

Eliminates some of the data in the image and therefore provides greater compression ratios than lossless compression.

Applied to video because some drop in the quality is not noticeable in moving images.

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Two types of CODEC (lossy):Spatial compression

a digital compression of video data that compresses the size of the video file by compressing the image data of each frame

Compression is done by removing redundancy from data in the same frame.

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Two types of CODEC:Temporal compression

a digital compression of video data that uses similarities of sequential frames over time to determine and store only the image data that differs from frame to frame.

Compression is done by removing similarity between successive video frames

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Flavors of file formats brand to choose:Microsoft’s AVI formatQuickTimeMPEGDiv-XWmv (Windows Media Video)

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Standards have been established for compression programs, including JPEG (Joint Photographic Experts Group) and MPEG (Motion Picture Experts Group).

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JPEG (Spatial)

Often areas of an image (especially backgrounds) contain similar information.

JPEG compression identifies these area and stores them as blocks of pixels instead of pixel by pixel reducing the amount of information needed to store the image.

These program reduce the file size of graphic images by eliminating redundant information.

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MPEG (Temporal)

The changes in the image from frame to frame.

Key frames are identified every few frames the changes that occur from key frame.

Provide greater compression ratios than JPEG.

Initially, it requires extra hardware for multimedia.

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Video Hardware and Software

VCRVCR

Video Overlay Board /Video Overlay Board /Video Capture CardVideo Capture Card

Video digitalVideo digitalEditing SoftwareEditing Software

MULTIMEDIA PCMULTIMEDIA PC

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Video Editing Software Incorporating transitions such as dissolves, wipes and spin. Superimposing titles and animating them, such as fly-in logo. Applying special effects to various images, such as twisting,

zooming, rotating and distorting. Synchronizing sound with the video. Apply filters that control color balance, brightness & contrast,

blurring, distortions and morphing.

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Advantages of using Video

Captures interestIncrease retentionClarifies complex physical actions and

relationshipsCan incorporate other media

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Disadvantages of using Video

Is expensive to produceRequires extensive memory and storageRequires special equipmentDoes not effectively illustrate abstract

concepts and static situations

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Summary

Digital video method is used for making and delivering video for multimedia.

Compression techniques help to reduce the file sizes to more manageable levels

Two types of compression lossless and lossy.

Standards for compression program are JPEG and MPEG.

Video

Technology

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