- 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:
- video capture (record)
- 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)
- reduced frame rate (AVI = 16 fps)
- dropped frames
- "tiny" windows (NOT TV sized)
- 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 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:
- NTSC (N.A., Taiwan, Japan)
- PAL (Europe, Australia, NZ, EXCEPT:
- 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