Flac - Nov 2005 - how to include FLAC in a CoreAudio wave player

Hi everyone,

I'm still new at this audio development thing in OSX
as all of my prior experience is in database
applications. I'm also new to C++ and the Xcode
environment, which makes things interesting as I
learn.

There is a CoreAudio wave player written in C++ to
which I would like to add FLAC playback support. I
have looked through the libFLAC++ API and think I have
an idea of what files/functions to use, but am not
really sure how to go about implementing them.

I think I want to use the file decoder class so I can
just pass it the name of the FLAC file I want to play
and use new, init, set and process_until_end_of_file
functions to do what I need. I have an idea of how
this will work in my head, but am having trouble
translating it to code. I also am having trouble
figuring out how this will hook back in to the
existing application.

I'm sure one of you with more experience can push me
in the right direction. I want to learn to do it
myself, but I also don't want to spin my wheels for
months at a time (as I have been, since I only do this
in my spare time) without signs of progress.

Thanks,
Matt


		
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On Fri, Nov 11, 2005 at 11:07:44PM -0800, Matthew DeNardo wrote:
> There is a CoreAudio wave player written in C++ to
> which I would like to add FLAC playback support. I
> have looked through the libFLAC++ API and think I have
> an idea of what files/functions to use, but am not
> really sure how to go about implementing them.
You might take a look at http://svn.xiph.org/trunk/xiph-qt/
which is some in-development code by Arek Korbok to add
CoreAudio components for vorbis and speex; that might give
you a place to start for implementing a flac component.

HTH,
 -r

--- Matthew DeNardo <matt_denardo@yahoo.com>
wrote:
> There is a CoreAudio wave player written in C++ to
> which I would like to add FLAC playback support. I
> have looked through the libFLAC++ API and think I have
> an idea of what files/functions to use, but am not
> really sure how to go about implementing them.
> 
> I think I want to use the file decoder class so I can
> just pass it the name of the FLAC file I want to play
> and use new, init, set and process_until_end_of_file
> functions to do what I need. I have an idea of how
> this will work in my head, but am having trouble
> translating it to code. I also am having trouble
> figuring out how this will hook back in to the
> existing application.
I don't know how deep you've gotten into the API docs,
but since the C++ library is mostly a wrapper around
the C one, most of the documentation is for at the C
level, but can be trivially applied to the C++ class
since the calls have similar names/signatures.  the
C++ just makes the C callbacks into virtual methods
mostly.

so I would say first look a
http://flac.sourceforge.net/api/group__flac__file__decoder.html#_details
and dive down into the individual functions for details (maybe you have
already done this).

there are also examples in the unit tests of how to
create a class derived from the file decoder; see
src/test_libFLAC++/decoders.c in the source distribution
and search for FileDecoder.  most of the code in there
is thousands of lines of tests but the actual class
setup is pretty simple.

it's hard to know how to help with hooking it into
the app without knowing the app.  the libFLAC decoder
is pull-based, i.e. one you process_until_end_of_file(),
control is only going to come back to you during
callbacks (mostly write) or end of stream.  if the
app is push based you will have to do frames at a time
into a fifo (see the source for the winamp or xmms
plugins), or use multiple threads.

Josh



		
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On 11/12/05, Ralph Giles <giles@xiph.org> wrote:
> On Fri, Nov 11, 2005 at 11:07:44PM -0800, Matthew DeNardo wrote:
>
> > There is a CoreAudio wave player written in C++ to
> > which I would like to add FLAC playback support. I
> > have looked through the libFLAC++ API and think I have
> > an idea of what files/functions to use, but am not
> > really sure how to go about implementing them.
>
> You might take a look at http://svn.xiph.org/trunk/xiph-qt/
> which is some in-development code by Arek Korbok to add
> CoreAudio components for vorbis and speex; that might give
> you a place to start for implementing a flac component.
>
> HTH,
>  -r
>
Well, the CoreAudio FLAC component is mostly ready and working. No
need to write it. It just needs a bit of refactoring, and I will add
it to the repository soon.

If this is a CoreAudio player it probably uses CoreAudio mechanisms to
handle media(audio) files. Hence, once the CAFLAC component is
installed, it should be quite simple (using CA API, not the Ogg/FLAC
libraries/frameworks directly) to make the player use that component
for FLAC-file decompression.

Hope this helps.
Arek