[Fwd: MPEG II Encoding]

[Terry Fox]

After tacos yesterday (6/23), some AMRAD members were treated to a discussion of
european Digital Amateur Television (DATV) from Prof.  Uwe Kraus, DJ8DW.  One of
their ongoing issues is the use (and cost) of MPEG encoding/decoding, especially
encoding.  They use the creative solution of using DBS receivers as the MPEG
decoders.  They are looking at the Fujitsu MPEG encoders and decoders, but EVMs
for that chipset are outside the average amateur's budget.

Unfortunately, I had to leave before the meeting was over, but while Uwe was
talking, I started thinking about where low-cost MPEG II compression chipsets
were, and remembered two potential sources.

One was the iCompression article I saw last year, the link to their website is
below.  The other is Tivo.  I have had one for almost two years, and have
purchased a second one to play with at work.  In the highest compression (lowest
bit-rate), the Tivo compresses to about 1 Gigabyte per hour.  I think that works
out to about 270 Kilobytes per second, or 2.2 Mega-bits per second.  This is the
same rough range that the Germans are working at.  I haven't had time yet to
look up the Tivo encoder and decoder chips to see if they can be throttled back
even more.  By the way, at this low compression rate, it is easy to see
compression artifacts, usually blockiness during scene changes or fades..

While we could also use satellite DBS/DSS receivers, my recollection is that at
least DirecTV (which I have) played with the MPEG II compression to  make it
non-standard.  I think they actually changed the transport stream, not the MPEG
compression algorithm itself.  If we could reverse-engineer those changes, then
using low-cost DSS dishes for receive is also a possibility.  Ripping into DVD
players is another potential decoding device.

Anyway, if the US wants to start looking at digital amateur TV (I'll call
"ATV-D" to avoid the "DATV" term which seems to be taken for another use), we
may have the tools to do low-cost compression.  Paul has been talking about a
multimedia repreater for a number of years, maybe this is just one use of that
device.

Next comes the frequency discussion.  Where, oh where do we put these rf-bits?
Finding a 200kHz-wide channel is hard enough, can we really find a set of
2MHz-wide channels within the spectrum the average amateur can effectively use?
I don't know the answer.  All I know is that it's hard enough doing 450MHz from
many locations, trying to do 2.4GHz is going to be self-limiting.

Hope that helps.
Terry

Alex Fraser wrote:

> I missed the talk. Is there any on net info on their digital TV project?
>
> Terry Fox wrote:
>
> >   ------------------------------------------------------------------------
> >
> > Subject: MPEG II Encoding
> > Date: Sat, 23 Jun 2001 18:22:10 -0400
> > From: Terry Fox <tfox@erols.com>
> > To: tacos@amrad.org
> >
> > This afternoon's talk was very interesting.
> >
> > I suggest we keep up with what they are doing, and possibly get one set
> > of systems when they become available.  I think 1296 MHz might be the
> > best place for this.
> >
> > How about looking at the Tivo for MPEG encoding and decoding.  Maybe we
> > can find some old Tivos at a good price, and wire into the encoder and
> > decoder.  Also, since Tivo uses Linux for control, we may be able to
> > decipher how to control the encoders and decoders.  At one time, Tivo
> > had the source code available on their web site.
> >
> > Another option might be a chip from icompression.  Last year, I saw an
> > article in Electronic Design for a new chip that iCompression was coming
> > out with that does both encoding and decoding.  At that time, it was
> > just coming out, and I haven't looked to see if the chip is out yet.  It
> > was supposed to be $29 in large quantities, but used a 456-ball BGA
> > connection....
> >
> > Terry
>
> --
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> ~~~~~~~~ Alex Fraser  N3DER ~~~~~~~~~~~
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