Re: ExtAudioFileRead: how to create AudioBufferList
Re: ExtAudioFileRead: how to create AudioBufferList
- Subject: Re: ExtAudioFileRead: how to create AudioBufferList
- From: William Stewart <email@hidden>
- Date: Mon, 20 Nov 2006 11:26:19 -0800
On 18/11/2006, at 7:25 AM, David Duncan wrote:
On Nov 18, 2006, at 05:34 AM, maximilian marcoll wrote:
ExtAudioFileRead needs an AudioBufferList for storing data in.
but i just can't figure out how to create an appropiate buffer list.
i can't allocate memory for the mBuffers field of the buffer list,
because mBuffers actually is no pointer.
if i don't allocate, it doesn't work either
(of course it doesn't - there is no memory for ExtrAudioFile to
write to.)
The idiom is a common one for allocating variable length arrays.
This can be done easily with malloc() and other byte-oriented
allocators like this:
mInputBuffer = (AudioBufferList*)malloc(sizeof(AudioBufferList) +
(numBuffers-1) * sizeof(AudioBuffer));
This is not quite correct and won't work correctly for 64 bit. The
correct way is to use the offsetof operator:
mBufferList = reinterpret_cast<AudioBufferList*>(new Byte[offsetof
(AudioBufferList, mBuffers) + (mNumberBuffers * sizeof(AudioBuffer))]);
We also have a couple of classes in the PublicUtility directory in
our SDK (/Developer/Examples/CoreAudio) - AUOutputBL is probably the
simplest one, then there is CABufferList
Bill
where numBuffers is the number of buffers you want in your
AudioBufferList. We subtract 1 since it already has 1 allocated.
Remember that C (and other C-like languages) don't range check
arrays, so you can just index to your hearts content, which is what
this relies on.
--
Reality is what, when you stop believing in it, doesn't go away.
Failure is not an option. It is a privilege reserved for those who
try.
David Duncan
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