[vorbis-dev] Reading OGG embedded in a pack file

[Conrad Parker]

Hi Ken,

by the sounds of it, you're dealing with a bunch of really short sound
effects, right? and you want to be able to grab one, decode it, and
send it off to play?

You want to be using vorbisfile's callback functions, including seek:

  http://www.xiph.org/ogg/vorbis/doc/vorbisfile/callbacks.html

Let's say you have a sound effect which you know starts at byte 10000
and ends at byte 25000.

You supply fake functions for seek, read and tell which make libvorbisfile
think that it's actually dealing with a 15000 byte long file; ie. you
translate seek requests by an offset of 10000 and you make any request
beyond 15000 look like an EOF.

You pass these functions to ov_open_callbacks() when you create your
vorbisfile handle, then you just use libvorbisfile as though you'd just
opened a single sound effect disk file.

another guy wrote some SDL_mixer support using liboggz+libfishsound, which
do similar stuff to libvorbisfile but are callback based (and can handle
multitrack, but you probably don't need that):

  http://www.dingoskidneys.com/fishmixer/

You'd want to check out OggzIO in the oggz api docs if you go down that
path, but it's the same kind of deal as for vorbisfile: you set up the
right callbacks, then just let the library do its thing.

Conrad.

On Mon, May 03, 2004 at 11:58:23PM -0500, Ken Rogoway wrote:
> Michael,
> 
> I respect your knowledge and apologize if I am trying to do something that
> is poor application design.  Having coded for over 20 years I would like
> to think that I should know better, but I am a bit stumped as to how I can
> have 100+ different OGG files inside a large package file, and then when
> needed go and grab a single OGG file from the package to decode it for
> the SDL_mixer which expects a properly decoded wave buffer.  If you have
> some thoughts on how best to approach this I would greatly appreciate your
> sharing them with me.
> 
> I guess my biggest problem is that I am trying to take two 3rd party
> libraries
> and make them work with a pack file scheme.  It sounds like I am being an
> idiot in my approach.  Please explain a better way to do this.
> 
> Sincerely,
> 
> - Ken Rogoway
> 
> > Okay.  It seems like this could have been solved by having a parm for non-
> > seekable streams that specified the size of the stream.  Regardless, I
> > understand
> > what you are saying and realize the limitations vs. what I am trying to
> do.
> 
> It's very rare to have a non-seekable stream where you know the size of the
> stream in advance - and it's almost completely useless. Such a parameter
> would just encourage poor application design.
> 
> In your case, the stream IS seekable - it's just that you're lying to
> libvorbisfile and telling it that it isn't seekable, to simplify your
> implementation.
> 
> This _seems_ useful to you because of limitations in some other part of your
> program.
> 
> 
> > I want to load the entire steam so I can pass off the decoded data to a
> > function
> > that plays wave data.
> 
> I suspected so. This is a flaw in your system - you shouldn't have to pass
> the
> entire stream all at once. You should seriously consider a different
> approach
> where you can decode incrementally and pass smaller buffers to the playback
> part of your program. This isn't usually hard to do.
> 
> Mike
> 
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