Re: QuickTime GS movie of jet fighter uploaded to ground

[dempson@actrix.gen.nz (David Empson)]

Supertimer <supertimer@aol.com> wrote:

> spec@vax2.concordia.ca (Mitchell Spector) wrote:
> 
> (snipped great explanation of movie conversion to GS)
> >I suppose you
> >could also write a PaintWorks $C2 player that could play
> >the frames as it reads it, but you'd need a very fast SCSI
> >interface and hardrive to keep it from getting choppy.
> 
> Now that's a novel idea.  Back when the Apple High Speed SCSI
> card was released, Apple used a movie to demonstrate the fast
> transfer of the interface card.  It loaded frames from disk as they
> were played.

They were full frames of super-hires graphics loaded directly into video
memory with the DMA circuitry, in a loop (easy to set up with the
firmware and the right documentation).

In theory, the High Speed SCSI card can get nearly 1MB per second
transfer rates using this method (on the IIgs - it is limited to half
this on the IIe).  Assuming it was producting 30 frames per second, it
would need to transfer 960 KB per second (30 times 32KB).

> Can't a $C2 player do the same thing using the same
> (or faster) interface card?

I don't think so.  The $C2 animation format has an initial 32KB frame
followed by difference frames which specify byte offsets and replacement
values.  This cannot be handled directly by the DMA engine of the Apple
card (possibly on a small scale, but not in general), and I expect the
RamFast's DMA scheme is simpler.

The $C2 format requires CPU processing to generate each video frame
after the first.

Of course, one could write a program which generated a sequence of full
video frames from a $C2 file, then use the Apple HS SCSI card to play it
at high speed.  The RamFast should be able to achieve almost the same
speed (it probably needs CPU interaction at the end of each frame of
video).

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand