lecture 07 razia nisar noorani digital video. basic digital video concepts cs118 – web engineering...

LECTURE 07

RAZIA NISAR NOORANI

Digital Video

Basic Digital Video Concepts

CS118 – Web Engineering

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Movie lengthFrame sizeFrame rateQualityColor bit depthData rate (bit rate)

Movie length


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File size is proportional to the movie length.Videos longer than 1 or 2 minutes cause long

download times.If it is a long video, consider to use streaming

video.

Frame size


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“Full-screen” video is 640x480 pixels.The most common frame size for web video is

160x120 pixels.Not recommend to use a frame size larger

than 320x240.The size depends on the CPU power and the

Internet connection bandwidth.

Image and Video?


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Frame rate


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Frame rate is measured in number of frames per second (fps).

Standard TV-quality video uses 30 fps.For the web, 15 or even 10 fps is more

appropriate and produces fair smooth quality for the user.

Commercial Internet Broadcasts are using 0.5, 0.25 frames per second.

Quality


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Many video-editors allow you to set the overall quality of the video.

The degree of compression controls the target quality.

The low or medium setting results a fairly high compression which is appropriate for web delivery.

Frame rate and quality are usually tradeoff in different applications.

Color bit depth


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The number of pixel colors in each frame affects the size of the video.

The file size of the video will be greatly reduced by changing the number of colors from 24-bit to 8-bit.

It sacrifices the image quality of the video.

Data rate (bit rate)


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This is the rate that the data must be transferred in order to ensure the video can play smoothly without interruption.

It is measured in kilobytes per second (K/sec or Kbps).

It can be calculated by dividing the size of the file (in K) by the movie length (in seconds). E.g. the video file size is 1.9MB 1900K Play 40 seconds long, Data rate = 47.5K/sec

Consider the Internet bandwidth!

Calculate space requirements of Video


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NTSC video (640 x 480 and 29.97 fps) Frame size = ([Pixel width x pixel height x bit

depth]/8)/1024 E.g. 200KB/Frame : 6.0 MB/sec 200KB x 30 fps = 6000KB/s, 6 MB/sec

PAL video (768 x 576 and 25 fps) E.g. 200KB/Frame : 5.0 MB/sec 200KB x 25 fps = 5000KB/s, 5 MB/sec

Video CODECs


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CODEC is “Compression/Decompression” algorithms.

The sound and frame images of a digital video must be compressed. The vast amount of data

Compressed in a number of ways Lossless and Lossy compression Spatial and Temporal compression

Video Clip Demo


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reference

Lossless and Lossy compression


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Lossless compression means no information is lost and the final file is the same as the original.

Most compression methods are lossy. Sacrifices some data from the file in order to achieve

higher compression rates. Use complicated algorithm to toss out some data that

is not discernible to the human eye or ear.

Spatial and Temporal compression


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Spatial (Intraframe) compression takes place on each individual frame of the video.

Temporal (Interframe) compression applies on a series of frames, it takes advantages of areas of the image remain unchanged from frame to frame. Relies on the key frames and delta frames. A key frame is placed once every second. E.g. 15 fps, a key frame once 15 frames.

Delta frame


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Video File Formats


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QuickTime Movie (.mov) Introduced by Apple Computer in 1991. First developed for Macintosh, now also supports the

PCs. Also supports streaming.

How to create? Most video editor, QuickTime Pro.

How to play? QuickTime plug-in or QuickTime player.

Quicktime


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http://www.apple.com/quicktime/gallery/cubicvr/times_square.html

RealMedia (.rm)


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Industry standard streaming format.RealPlayer for playback.RealServer for serving streams.RealProducer for creating .rm files.Good for

Long-playing video or broadcast to many people.

How to create? RealSystem Producer

How to play? RealPlayer (Free), RealPlayer Plus

(Commerical)

Windows Media (.wmv/ .asf)


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Created by Microsoft, closely integrated with Windows OS.

Support Windows Media Video (.wmv) and Advanced Streaming Format (.asf) and other formats (.avi, .mpeg, …)

Also support streaming.How to create?

Windows Media Encoder, Windows Media AuthorHow to play?

Media Player in Windows OS

AVI (.avi)


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Stands for Audio/Video Interleaved.Introduced by Microsoft in 1992.In a AVI file, the audio and video

information are interleaved every frame.

Good for Short web clips, high-quality video

How to create? Most video editing tools.

How to play? Windows Media, QuickTime, etc.

Video Clip Demo


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reference

MPEG (.mpg/ .mpeg)


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Created by Moving Picture Experts Group (MPEG).

Supports 1) Video, 2) Audio, 3) Streaming.Extremely high compression rates with

small quality degradation (lossy).MPEG-1 : VHS qualityMPEG-2 : HQ standard for TV broadcastMPEG-4 : Very HQ for AV compressionMPEG can be compressed by using three

schemes: Layer-I, Layer-II, Layer-III.

Official MPEG page


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MPEG Comparison


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MPEG-1MPEG-1 MPEG-2MPEG-2 MPEG-4MPEG-4

Standard sinceStandard since 19921992 19951995 19991999

Default Video resolution Default Video resolution (NTSC)(NTSC)

352 x 288352 x 288 640 x 480640 x 480 640 x 480640 x 480

Max. Audio Frequency rangeMax. Audio Frequency range 48 KHz48 KHz 96 KHz96 KHz 96 KHz96 KHz

Max. audio ChannelMax. audio Channel 22 88 88

Regular data rateRegular data rate 1380 kbit/s1380 kbit/s 6500 kbit/s6500 kbit/s 880 kbit/s880 kbit/s

Frames per sec (NTSC)Frames per sec (NTSC) 3030 3030 3030

Video QualityVideo Quality SatisfactorySatisfactory Very goodVery good Very GoodVery Good

Hardware requirement for Hardware requirement for encoding/decodingencoding/decoding

LowLow MediumMedium HighHigh

Flash & Shockwave


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Advantages: File sizes are small Image quality is high It uses streaming technology It uses high-quality streaming audio It is scriptable

Disadvantages: A plug-in player is required Expensive authoring software Problems on printing their content

Summary


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Discuss the basic digital audio/video terminology.

Introduction to different formats: WAV, MP3, QuickTime, RealMedia, Windows Media, AVI, MPEG.

To deliver long-playing audio/video or live broadcasts, you should choose one of the streaming media.

Flash and shockwave are popular and appropriate format for the Web.

lecture 07 razia nisar noorani digital video. basic digital video concepts cs118 – web engineering...

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