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readme.txt
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1997-03-28
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Readme for OS2ENC/OS2DEC v.0.1:
OS2ENC/OS2DEC is a freeware Mpeg audio Encoder/Decoder for OS/2.
It was compiled with Gcc, so it requires that you have the emx 0.9c
runtimes installed on your system.
As it's only an encoder/decoder, you don't need to have any multimedia
hardware installed. (you'll need it if you want to sample some songs
and test it by yourself, obviously)
This version is a raw port of the public source code available at
ftp://ftp.tnt.uni-hannover.de/pub/MPEG/audio/mpeg2/software/technical_report/dist08.tar.gz
So don't expect ANY performance.
Anyway, it's the first layer-3 encoder available for OS/2 at this
present time and it's not crippled (in the general meaning of the term).
In fact, it's crippled by its own limitations, especially by its speed !
Installation:
------------
Just unzip the file in an empty directory, say x:\mp3\os2enc\,
make sure you have the amx 0.9c runtimes installed on your computer,
make sure you are in an OS/2 session (no, it won't work under Dos or
the nasty windoze).
Last thing to do is to set an environment variable for the translation
tables.
Either type SET MPEGTABLES=x:\mp3\os2enc at the prompt for this particular
session, or put it in your CONFIG.SYS (and don't forget to reboot for
changes to take effect)
Features:
--------
The encoder/decoder is fully MPEG-1 and MPEG-2 compatible, for the
three available layers (Layer-1, layer-2 and ... layer-3).
As MPEG-2 introduces multichannel notions, it's only been tested
for being compatible with MPEG-1, and it's probably the only thing
you'll need, as MPEG-1 is used for 44Khz, stereo, 16b compression,
that means CD-quality. MPEG-2 is used for lower sampling frequencies
(ie: 22.05 Khz or below)
The import format for the sound files is PCM, which means a raw
sound file, with signed integer and 16bits. This version doesn't
handle WAV files yet.
The output format of the decoder is either raw (PCM) or AIFF.
Hint: if you don't know how to make a PCM file, just take a WAV file
and cut the first 44 byter of it, it should work.
The decoder decodes almost any MPEG-1 and -2 compliant files.
The encoder lets you chose between the 3 available layers, the
output bitrate, and some other options:
1. First, you'll enter the input filename of your sound file
2. Then, the output filename, default is <input_file>.mpg
3. Then, you'll need to enter its sample frequency in KHZ:
correct values are 44100 (default) or 22050, 11025 not available yet
If you chose 44100 KHz, the encoding algorithm will be MPEG-1
If you chose 22050 KHz, it will be MPEG-2
4. Then the layer you would like to use:
Layer-2 is designed for an output bitrate of 128 Kbps/channel
Layer-3 is designed for an output bitrate of 64 Kbps/channel
So, depending on the type of compression you need, use layer-2
or layer-3
Layer-2 gives a lossless compression of 6:1 for a 256 Kbps
bitrate for a stereo signal.
Layer-3 gives a lossless compression of 10 to 12:1 for a
128 to 112 Kbps for a stereo signal.
This means, if you use layer-3 at 112 Kbps on CD-quality sound, you'll
get a 1 Mb/mn of audio sound with the same quality as a Wav file, which
sucks 10 Mb/mn of music... Ain't it cool ... ! :)
5. Next is the mode you want:
Available are (s) for stereo (default)
(j) for joint-stereo (fake stereo from both channels)
(d) dual channel
(i) single channel (use this one if the input is a mono
signal)
For some reasons, joint-stereo doesn't work yet, so forget it ...
6. Then chose the psychoacoustic model (uh ? ..):
Don't worry, here's the hint, use '2' for layer-3 and '1' for layer-2
(caution: '1' is the default, think about it when you use layer-3)
7. Then enter the bitrate for the output file (this value is the global
output bitrate, for both channels).
Common values are 384 - 320 - 256 - 192 - 128 - 112 - 96 - 64 - 56 - 32
You can try layer-2 at 256 for high quality, 192 with a little loss
For layer-3, preferred values are 128 or 112 Kbps for lossless quality.
8. Then, you'll be prompt for the de-emphasis ... use <n>one .
9. Then you'll be prompted for some adding stuff, the private bit, error
protection, copyright ,etc... chose what you want.
10. And yet, go for it... you'll get a summary of the options you chose,
and you'll 'see' the coding. Remember, encoding takes a looooooong
time, don't blame me for it right now, okay ... :)
Now, even if you don't have a descent player, or if your computer is not
a Pentium and though can't play a mp2 or mp3 file in real-time, if you
want to keep some wav files and save some hard-disk space, use this
program as a compressor... It achieves far better than Rar or Zip,
believe me.
You can also use these options at the command-line prompt, just
type 'encode -h' to get help.
To-do list:
----------
- test every option (esp. the MPEG-2 algorithm)
- fix the joint_stereo option and 11025 Khz
- add input/output file formats (Wav,AIFF,etc)
- change the defaults dialogs according to the layer choices
- change the verbose output to a descent one
- optimize the code (yeah, that's the main stuff)
History:
-------
February, 1 1997: version 0.01
First beta version
Acknowledgments:
---------------
This program is provided 'as is', which means I won't be responsible
for any thing that turns wrong (as Murphy said, 'if something can go
wrong, it will')... Obviously, it won't wipe out your hard-drive
(on the contrary, if your hard drive is full of wav files, it will
clean it up safely). Be careful when you uncompress mp3 files,
remember layer-3 compresses up to 12:1 so if you have a 5 MB mp3 file,
you'll get a 60 MB WAV file (AIF in fact).
That's all folks... enjoy it, feel free to distribute it to your
OS/2 friends, and look for the next releases of this software.
--