CPSC 461: Copyright (C) 2003 Katrin Becker Last Modified June 2, 2003 11:54 PM
FILE FORMATS
Multimedia / Video

Main Data File Format Types:

Documents (text; word-processor; LaTex; postscript; etc.)
Electronic Data Interchange (EDI : formats for e-commerce)
Scientific
Graphics (raster; vector)
Audio (sound & voice)
Animation (moving pictures)
Multimedia (video; combined)

ALL moving pictures (film, broadcast, video, etc., depend on "persistence of vision" ( eye's response lag -> after-images ).
We SEE series of still pictures: we PERCEIVE moving objects.
Requires pictures flashed at a rate higher than "fusion frequency".
Fusion frequency depends on brightness of image relative to viewing environment - normal is about 40 images per second.

- a little low = flicker
- a lot low = stills

Film = 24 frames / second (projector flashes twice for each frame)
NTSC broadcast standard = 30 frames / second (images interleaved)
PAL & SECAM = 25 frames / second
Computer Monitors: 12-15 frames per second works because of high (variable) refresh rate.
2 ways to generate digital moving pictures:

1. video capture (record)
2. generate each frame

Just like images: natural source VS computer generated (video VS animation)
Video places considerable strain on current computer systems (Q: How many computers were used to do the rendering for Shrek?)
- part of the problem is that experience of consumers is primarily (still) based on broadcast video
- video intended for computers is (typically)

1. reduced frame rate (AVI = 16 fps)
2. dropped frames
3. "tiny" windows (NOT TV sized)
4. exhibit visible artifacts (resulting from compression)

The single biggest problem with video is the amount of data that must be processed.
NTSC:

each frame = 640 X 480 X 3 bytes = 900 Kbytes
1 second = ~26 Mb
1 minute = 1.6 Gb
LOTR = ? (~>200 Gb!!)

PAL is higher resolution (Q: What's resolution?) so 768 X 576 X 25 fps = 1.85 Gb/min.
You'd pretty much need a RAID if you wanted to keep any movies.
Q: What's the key feature with moving pictures?
They have to come one after the other.
They have to be displayed fast enough to be perceived as continuous motion.
The ONLY answer: compression (note fast play-back is a biggie here).
For internet use or playback from CD-ROM we must use SEVERE compression
PLUS
limited frame size (witness "dancing postage stamps")
This is not possible without loss of quality.
The other end of this: capture : to capture in real-time usually requires dedicated hardware to do the compression stuff.
MULTIMEDIA:
- files can include text, audio, video
Animation data: (FLI, GRASP, AVI, etc.)

- "flip-book" images
- compress using RLE & differencing

Digital Video:

- broadcast video (TV signals)
- requires high-speed interface (IEEE 1394 - code name:_____________)

Q: What does DVD stand for?

3 main standards:

1. NTSC (N.A., Taiwan, Japan)
2. PAL (Europe, Australia, NZ, EXCEPT:
3. SECAM (France, USSR(ish))

Asia, Africa follow colonial history.

South America: very confused.

These standards detail how colour TV is coded for broadcast. Typically, each frame is divided into two "fields": 1 of even "lines" and one of odd "lines".
For digitization, fields are sometimes combined, but when it was analogue, each field was a different instant in time (1/60 sec.)
When there is very rapid motion, combining two fields into one frame can have undesirable effects. E.g. a flash of light (which might only appear in a single field); other rapid movement results in artifacts. (Thrown ball)

CPSC 461: Copyright (C) 2003 Katrin Becker Last Modified June 2, 2003 11:54 PM