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- Newsgroups: comp.sys.mac.misc
- Path: sparky!uunet!zaphod.mps.ohio-state.edu!rpi!batcomputer!lynx@msc.cornell.edu!leah.msc.cornell.edu!maynard
- From: maynard@leah.msc.cornell.edu (Maynard J. Handley)
- Subject: semi-technical QuickTime info required...
- Message-ID: <1992Nov8.091942.8451@msc.cornell.edu>
- Sender: news@msc.cornell.edu
- Organization: Cornell-Materials-Science-Center
- Date: Sun, 8 Nov 1992 09:19:42 GMT
- Lines: 48
-
- I've been playing with QuickTime a bit and wondered if anyone out there
- could help me with the following few questions.
-
- 1) All right. I know the two principals for JPEG compression are taking
- DFTs of 8x8 cells and discarding hi-frequency info, along with decomposing
- the image into YUV planes (or something like them) and sampling color info
- at a lower frequency than lightness info.
- Based on the way Apple and others claim the Apple animation compressor
- should be used, I would guess that it performs RLE encoding. Does it just
- do the standard PICT RLE encoding? Is this simply along the x direction, or
- is it done along both x and y directions?
- "None"-encoding. Is this truly none, or does it do the basic PICT
- compression?
- Apple graphics---what gives here? The only thing I know about this is that
- I have yet to find anything for which it works nicely. Does it insist on
- the system pallette? Does it needs globs of the same color?
- Apple video. Looks like it does the JPEG scheme of blocking, but what else.
- I
- guess it's not simply JPEG diddled a bit, cause of the speed.
- The new Apple compact video. What's this based on? Wavelets? It produced
- artifacts unlike anything I've seen elsewhere.
-
- 2) Is ANY form of inter-frame compression performed when making movies? I
- thought that when you gave a key-frame rate, that meant that each key-frame
- was stand-alone, but other frames were based on inter-frame encoding. But
- I've tried varying the key-frame rate from zero to every frame and in
- between, and the file size seems to change each time by about 2K, which
- seems to imply not much is happening. The various key-frame rates also
- seemed to have no effect on quality of playback, either forwards OR
- backwards. Is this just a bogus field that will be used in later versions
- of QuickTime?
-
- 3) What is the major bottleneck in playback speed? It seemed to me that
- this would be decompression. However on my SE/30 a (grey-scale 150x200)
- movie made at
- 15fps plays back rather more smoothly when compressed with either Apple
- Animation or Apple Compact Video than with no compression, and compact
- video gave better playback than animation. (At ten fps all three schemes
- were equal so I guess the machine wasn't yet maxed out.) Is this because in
- fact most of the time is data transfer time, and the compressed movie have
- to pull less data off disk? Or is it some effect of grey-scale? I haven't
- yet got around to experimenting seriously with color movies so I don't know
- what would happen there.
-
- Thanks for any info people may have on this matter, both empirical and the
- official Apple word.
-
- Maynard Handley
-