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Lecture 2

Computer Science 1033A/B Lecture Notes - Lecture 2: Digital Media Player, Indeo, On2 Technologies

Computer Science
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Video: a sequence of still images that create the illusion of movement when played
Movies = 24-30 fps Computer Displayed Vide0 = 12-15 fps
NTSC (tv) uses 29.97 fps.... (used to be 30, but they decreased to accommodate for colour
Before 1996, all TV used interlaced display:
-The screen would develop every other line (480 in total) and then go back through and do the
rest of the lines so that the entire picture would show up (rather than just half at a time) because
it could not develop fast enough - each pass is called a field
NTSC (National Television System Committee) standards:
720 by 480 pixels
Frame Aspect Ratio 4:3 -> pixels are distorted (rectangular) because 720:480 is a
3:2 ratio
High Definition Ratios are 1440 x 1080 and 1280 x 720
New TV's have 720 or 1080 lines of pixels and use PROGRESSIVE (not interlaced)
Sampling Process: each frame is sampled into discrete samples and each sample becomes a pixel
-(more samples/pixels = better quality but bigger file size)
Quantization Process: each pixel is assigned a colour (from 1bit - 24 bits)
Digital video can be displayed on computer (no NTSC standards), TV or DVD
Camcorders are typically used to capture and later display video
-Analog Camcorder -> must convert to digital before put it on computer
-Digital Camcorder -> no converter needed (mostly used now)
Does some compression inside the camcorder (DV25 is most common)
DV25: Pixel = 720 x 480 (3:2), Frame Aspect = 4:3 or 16:9, Data Rate = 25 mb/sec,
Frame Rate = 29.997, Colour Sampling = YUV 4:1:1
Video use YUV (YIQ) or YCbCr colour compression
-Y -> brightness (luminance) UV (or CbCr) -> Colour/Hue (chrominance)
-Brightness is more important than colour (UV) will be compressed, but brightness (Y) won't be
-4:4:4 is fill colour and brightness, 4:1:1 is common because it is 50% compressed by decreasing
To get video to computer: Apple uses Firewire, PC uses USB
Master/Slave connection (need to connect to a computer)
Compressing Video
-Video: 1555200 pixels per frame x 24 bit colour x 30 fps = 133MB for just 1 second of video
-Audio: 188 KB
-So much storage for 1 second of video
-Without compression, DVD could hold 35 seconds of video
Data Rate: amount of video processed per second
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