Re: MPEG Player

From: Richard Elwell <>
Date: Thu, 11 Dec 1997 09:34:31 +0000

I can now explain what was going on with my MPEG playing problems.

I must reiterate that my Falcon's setup is new to me and there are
still aspects I don't fully understand. Thanks to this I have learnt
a few things.

Firstly my mentioning of NVDI as being a possible source of problems
was based on the fact that the change from v2.5 to 4.11 is one of the
obvious differences and it is involved in graphics. I doubted that
was the cause but you never know.

The confusion lay in the fact that not so long a go I could play a
particular MPEG at about 12fps and now, with no changes to the TT-RAM
flags it was suddenly playing at 3fps. Setting both TT-Mem and
TT-Prog flags gave an fps figure of over 12 but a black screen.

I changed various parts of the set up and found myself able to get
back to a visible 12fps. But I changed too much too quickly so I
couldn't tell what was the cause so I back tracked more slowly and
worked it out.

If I say DMASnoop a lot of you will work it out straightaway. In
which case you can probably stop reading right here.

DMASnoop was in the autofolder of my new setup, I knew that
it would be there for a good reason and it certainly didn't seem to
be doing any harm. So I never investigated exactly what it was doing
and if there were any possible side effects.
I now know what it does and the side effects.

For those that don't know it is a prog that helps reduce errors on
DMA devices like SCSI equipment and the floppy disk drive. It makes
the ST-RAM non-cacheable. So any progs running in ST-RAM will be
run as though the CPU caches are off, making them much slower.

I found the in order for PlayMPEG to display anything it needs to
have the TT-Prog flag unset, so the prog will run in ST-RAM. The
TT-Mem flag can be set happily enough. With DMASnoop installed it is
running with the 040's caches and therefore is very slow.

What does strike me as odd is that a JPEG viewer I use sometimes,
JpegDSP (by D. Oldcorn) must have it's TT-Mem flag unset for it to

So PlayMPEG and JpegDSP work in fundamentally different ways?

If DMASnoop effected JpegDSP I would have investigated the problem
much sooner.

One thing that came out of this is that Griff would appear to be with
us. I hadn't seen you here before Griff. I don't suppose your
developing PlayMPEG any further? An AB and multitasking friendly
MPEG player that plays all frames would be very welcome.

I hope my explanation made sense. If not, or it is wrong, then let
me know.

Received on to. des. 11 1997 - 12:14:00 CET

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