From: Dale_Adams@gateway.qm.apple.com (Dale Adams)
Newsgroups: comp.sys.amiga.advocacy
Subject: Re: Comdex/Quicktime released for the PC
Date: 14 Dec 92 21:09:45 GMT
Organization: Apple Computer Inc.

In article <1992Dec14.114702.4604@memstvx1.memst.edu> 
cse_stu@memstvx1.memst.edu writes:
> I find it hard to believe that your Quadra can do 90 fps at 640 x 480 8 
> bit.  At that size screen you are talking about moving 256k per frame for 
> a full frame change which is worst case but it does happen. Your 90 frames 
> per sec is best case if there is a lot of compression.

Of course every pixel in the entire 640 x 480 image is not being updated 
every frame.  Any animation program which requires you to update the entire
image on every frame is inefficient at best.

However, note that the Quadra 950 frame buffer is capable of burst (i.e., 
'040 quadlongword burst cycles) transfer rates of well over 40 MB/sec.  
Tranferring a 680 x 480 8-bit image in 1/90 of second is a transfer rate 
of just under 28 MB/sec., which is certainly less than the maximum 
transfer rate.  (A 640 x 480 screen is 300K bytes, not 256K, by the way.)  
Of course there are inefficiencies involved.  You've got to get the new 
image data from someplace (main memory, in this case),  arbitrate for the 
bus if necessary, allow for VRAM refresh cycles, etc.   So real world 
transfer rates are quite a bit less than the theoretical maximum.  
(Although the Q950 frame buffer could sustain a transfer rate of over 40 
MB/sec. if there were an '040 bus master which could supply the data this 
fast - say PDS card which did MPEG decompression in hardware, for example.)

> I work on mac's and amiga's and when the program tells you that you are 
> doing 30 frames a sec it will not allways give you that output. I can test 
> the amiga easily by recording the animation onto videotape where I can step 
> through each frame to see if there are any changes. On the mac you are not 
> as lucky but if you can go to video tape that will be the real test.

The Quadras will produce NTSC or PAL timing so the video output can easily 
be sent to videotape.  (You do need an external RGB-to-composite converter 
to produce color composite video.)  I haven't tried this.  It sounds like 
an interesting test, though.  I have simply asked the animation program to 
play back at the maximum rate it can.  The output rate is definitely 3 
times the rate of a slower Mac whose maximum frame rate is 30 fps using 
the same software.  Slower Macs scale similarly.

> I've seen a Quadra running quick time and the sales guy said it was 30 
> frames per sec and 24 bit color but when I looked at
> the picture it was at best 10 or 12bit color and 8 to 10 frames per sec.

I never said I was using QuickTime.  If you're trying to get the maximum 
frame rate possible, QuickTime is not what you want to use.  And never, 
never believe the sales guy.  (Although using QT 1.5 I can playback 320 x 
240 animations at 30 fps on a 16 bit/pixel screen.)

> I should know because I have been dealing in animations for the past 5 
> years and I can tell 30 frames per second and I have never since any mac 
> that is able or has the specs to have full frame rate, full screeen 
> animation.

Then meet my Quadra 950.  (Maybe you haven't been using the right 
software?)

- Dale Adams
Newsgroups: comp.sys.amiga.advocacy