[Sub-sonic-development] SUB-SONIC updates/info

[<Do...@as...>]

Hello, I'm writing this e-mail to welcome on the new members of our
development team and get the current ones up to speed on the progress of
SUB-SONIC.

Since Saturday, concentrated development of SUB-SONIC is in progress. We're
hoping to provide you all with the core system on which to work on over the
next week. I've been working on a few plugins which I'll be trying to get
onto the CVS and released soon.

Ok what I'm going to do now is give a good break down of the system and
what's going on with it so that everyone is up to speed and has a basic
understanding of SUB-SONIC.

SUB-SONIC General
-----------------
The general idea behind SUB-SONIC is that there is a core system and a
series of plugins. The core system provides the architecture of the entire
system, it must handle audio input, process it with any effects requested
and then send it to it's output destination. The plugins are the actual
pieces of code which perform their unique part of each stage. There are
input, output and effect plugins. A input plugin will take a source usually
a file or data stream and turn it into a stream of uncompressed audio data
for the core to use. The effect plugin will apply a real-time effect on an
incoming audio source before it goes to the output destination. Finally the
output plugin takes the final mixed audio and passes it to the output device
which can be physical or computer based e.g. soundcard or disk file.

SUB-SONIC core
--------------
This component has mostly been developed by Dean Bilotti and Lourens Veen, I
have provided advice and an explanation on how to implement the audio side
of things but they have designed and produced the code. This component is
the most system dependent part of the system. Although we've coded it to be
as portable as possible, inevitably each platform's multi-threading works in
a different way as well as other features, therefore a certain amount of
porting will be needed of the core for each platform. A certain portion of
the efficiency and power of the overall SUB-SONIC system lies within the
core therefore there is always plenty of scope for improvement there.

As it stands presently SUB-SONIC is an entirely raw audio data based system,
this covers most music systems but some types of music systems currently
can't be implemented very well. For example MIDI can only be implemented as
a software synthesiser as there is no way for SUB-SONIC to get music data to
output devices, therefore a data layer would be required for that.

Input plugins
-------------
Input plugins in SUB-SONIC have more of a say in the way they want to
operate in compared to other APIs like Winamp. We've designed them to be
flexible so that an author isn't forced to write to a constrained
architecture. If I recall from looking at Winamp's API you had to provide
audio data in the same way an MP3 would generate it, which I found
potentially troublesome if the music system did not lend itself to that form
of data output.

The input plugins function by specifying their output audio format (e.g.
44.1Khz, stereo, 16-bit) and then providing a stream of audio data in the
specified format at the request of the SUB-SONIC core. At the moment the
input plugins data passing system is going for a bit of a redesign.
Currently we expect input plugins to produce a time length of data as their
input into the core but we are extending this so that plugins can push out
an arbitrary quantity of audio data which will then be arranged into
suitable blocks of audio by SUB-SONIC.

Output plugins
--------------
These will vary between portable and system dependent. Output plugins
usually deal with taking the mixer output and relaying it to the soundcard
either directly or via the appropriate API for whichever platform. The
plugins can choose whether or not to provide their own mixing code to
replace SUB-SONIC's built in mixer. This is designed mainly to allow for
hardware mixing. Each platform that SUB-SONIC gets ported to is going to
need at least one plugin of some sort to get the output of SUB-SONIC to the
computers audio device.

Effect plugins
--------------
As it stands the details of these are still a little sketchy. Effect plugins
are designed to allow you to apply audio effects (aka DSP effects) to a
stream of audio therefore adjusting the final audio in some way. As it
stands you will apply effects to the individual streams of audio and as yet
there are still design issues with applying effects to the mixed audio.
Effect plugins are our least needed area of development at the moment as
it's not an overly critical part of the system for the time being.

-------------------------------------------------

Hopefully the above summary should give you all an idea of roughly how
things work under the present design, if you wish to add design comments
feel free to do so. The actual development state of SUB-SONIC varies.

The core has been through an R&D stage, we had several trial versions
developed. After a few days discussion with Dean we are now working on what
we hope should become the final version of the core.

I've been working on 3 input plugins based on an old R&D version of
SUB-SONIC. They are as follows:

IMF - Intermediate Module Format
This is a multi-format module player. Presently only a few formats are
supported and a few of the pattern effects are missing but the system works.
This plugin will be needing a lot of further development and I hope to
document it in detail soon. The source code is very well commented.

Wave plugin
This just plays a standard raw PCM data Microsoft wave file. Further
enhancements should either use the ACM with running on Windows or we should
implement our own version of some of the ACM formats so that they can be
played on other platforms (e.g. MP3, ADPCM).

EA Audio plugin
This is a plugin written to play back music in Electronic Arts own audio
format found in many of their games. Presently we've got the uncompressed
audio working fine but the ADPCM code doesn't seem to work properly.

AAC plugin
I've started a bit of work on trying to implement the MPEG2 AAC audio format
as plugin. This code does not function yet as I've only done some initial
coding.

--------------------
So now you all know about SUB-SONIC I guess your wondering where do we go
from here. Well that all depends on what you the development team want to
do. This is a free project done in what I assume is everyone's spare time
therefore you contributions should be what interest you the most.

On the plugins side we have many formats to support. I'm not sure what
approach to take with things like MP3 as there are several choices. We can
either based the plugins on an existing project's decoding library such as
LAME, write our own based on the ISO sources or write our own from scratch
using the actual ISO standard. The amount of work require of course varies
greatly amongst those options. Some plugins are going to need only a little
bit of effort, others are huge jobs. IMF for example is almost like a
project within itself.

The core will need porting as soon as something solid and stable is ready
and there are always design obstacles that need to be addressed and overcome
with the core system itself.

Feel free to ask questions, suggest things to do etc. I hope we can all get
into the development of SUB-SONIC soon.

Doug

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Douglas Gore (do...@as...) ICQ: 15620154
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SUB-SONIC project manager
http://www.sourceforge.net/projects/sub-sonic/
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