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

Thu May 6 00:10:02 PDT 2004

Seems as it would be a very good idea to supply some sort of helper function
that takes a filepointer (from an archive for example) or a pointer to
memory and a start- and end - offsets to the positions where the ogg in that
archive / memblocks starts / ends and creates the necessary callback
functions. For passionate c programmers like you ogg develprs, callbacks
seem to be the most natural thing to solve such problems, but for beginner
programmers or hobby game programmers its always a big barrier to start
coding such. Ok, argument would be not to bloat the api, but whats the use
of a lean api, when people who wish to use ogg in their programs first must
start long threads or fiddle around be themselves to get an idea whats going
wrong and why ogg behaves so strange at first sight.

Something like this:

extern int ov_open2(FILE *f,OggVorbis_File *vf, long start_offset, long
end_offset, char *initial,long ibytes); 

And you would have much less traffic on vorbis-dev at xiph.org ;)

Greetings, andre

<p><p>> -----Original Message-----
> From: owner-vorbis-dev at xiph.org 
> [mailto:owner-vorbis-dev at xiph.org] On Behalf Of Monty
> Sent: Donnerstag, 6. Mai 2004 01:37
> To: vorbis-dev at xiph.org
> Subject: Re: [vorbis-dev] Reading OGG embedded in a pack file
> 
> I was about to suggest the same thing, but I see Conrad has 
> beaten me to it.  In case it wasn't clear from what Conrad said...
> 
> Just set up the fake stdio callbacks to pretend that the 
> given section of your file that is an Ogg archive is the 
> whole file.  So long as the callbacks act like 
> seek(SEEK_SET,0) is the beginning of the ogg 'file'
>  and seek(SEEK_END,0) is the end of the ogg 'file', 
> Vorbisfile will function as if that Ogg archive in the larger 
> file is a standalone Ogg file.  make sure the 'read' function 
> doesn't allow reading past the end either.
> 
> Sorry for letting this thread go on so long without this 
> suggestion coming up, I was on vacation :-|
> 
> Monty
> 
> 
> On Tue, May 04, 2004 at 03:43:35PM +1000, Conrad Parker wrote:
> > 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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