A Quick Look at MPEG3 Audio

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                        A Quick Look at MPEG3 Audio
                             By:  Jason Compton 
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I've been meaning to do a "Fun with video streams" feature, and was well on
my way to getting comfortable with the new QuickTime, AVI, and MPEG players
for the Amiga when something else came up, and in some ways it's even
better.

It's called "MPEG3", "MPEG Layer 3", "MPEG Audio" or sometimes just "mp3".
An MPEG3 file contains 16-bit audio data that has been massively compressed
(by a factor of 9 or more) and can be played back directly from a hard
drive.  At 44.1khz, a sampled song from CD can take up 50 megs or more.
Applying MPEG3 to the file can result in something more in the neighborhood
of 5 megs.

On the Amiga, we don't quite have the luxury of 16-bit playback, but if you
have a sufficiently fast system, you can get MPEG3 playback which still
sounds quite good.  You will want an 040 to really get good results,
however.

Presently, I'm using Stephane Tavenard's mpega 2.2, which you can find on
Aminet in mus/play as mpega.lha.  Other playback and decoder programs are
also on Aminet, in mus/play and mus/misc.

The principle behind MPEG is beyond the scope of this article, but the
compression scheme is being used for all sorts of high-speed video and
audio transmission and delivery, including VideoCD and the new wave of
"DVDs".  MPEG Layer 3 audio is a deeper level of compression than
previously used, and has made it possible to put CD quality sound in a
reasonably sized file.

The implications are of course that you can store an entire CD on a small
hard drive partition or even a Zip disk.  A Zip's 100 megs are more than
enough to contain all the data of a 74-minute CD.  The extended implication
is that a CD-ROM could actually store multiple CDs on it, providing you
were willing to play it back through a computer rather than a regular CD
player.  Whether or not this technology will catch on for a new breed of
CD players remains to be seen.

Because MPEG audio files have reached manageable proportions relative to
modern data transmission speeds (at about 3-6 megs of data for a typical
"radio" length song) 28.8 and 33.6k modems are suitably equipped to make
trading MPEG3 files over the net a reality--which is where things get
interesting.

There are literally hundreds of MPEG3 Web and FTP sites out there, but the
entire practice is rather objectionable from a legal standpoint.  Record
companies would rather have you buy their CDs than swap MPEG3 files with
the rest of the world--but they are out there if you look.  My cursory
inspection reveals an awful lot of Spice Girls and techno and not much of
anything I'd like to listen to.

If you want to roll your own, you have some options.  There are packages
for the Amiga that will allow you to create your own MPEG3s from a
digitized source.  However, MPEG3 compression is very, very time consuming.
I have not yet tried using an Amiga to do the compression.  Instead, I put
the P-100, which typically sits around as a game machine, to work.  There
is a program which will digitize a .wav file directly off of a CD-ROM
drive, and another which does the MPEG3 compression.  All told, the entire
process takes about 11-12x longer than the length of the song to complete.
I then take the resulting file over to the Amiga and play it back.

To get similar results on the Amiga you'd want to use a reliable sampling
program and preferably one that could get you reliable 16-bit results over
a long period of time.  (A cheapie homebrew parallel port digitizer is not
the ticket here.) Then be very very patient as the compression goes to
work.

I'll say this: I'm glad I've got a Zip drive now or else my hard drive
would be getting rather full.  In a way, it's a silly novelty--particularly
if you already have the CDs, why in the world wouldn't you just play them,
instead of the MPEG3 file?  Well, if you don't own them it's a good way to
sample CD-quality tracks without counting on radio DJs.  If you do own
them, if you travel with your computer it saves you the trouble of packing
your CDs.  And face it, like so many other things we do with computers, we
do them because we CAN.  MPEG3 is a very neat "Hey, look at what we CAN do"
technology with some very serious real-world implications which will likely
make existing "IPhone" and "AmiPhone"-type projects look and sound silly in
retrospect.

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