Re: [CoreAudio] General Question about Conversion
Re: [CoreAudio] General Question about Conversion
- Subject: Re: [CoreAudio] General Question about Conversion
- From: William Stewart <email@hidden>
- Date: Tue, 3 Jan 2006 12:29:36 -0800
There is also a simple example code project (ConvertFile in the
Simple folder of the latest SDK) that does not strive for the
generality of the afconvert code, but rather seeks to provide a
straight forward listing of the use of both the AudioConverter (data
conversion) and AudioFile (file read/write) APIs.
This example provides two versions that are functionally equivalent -
one uses the ExtendedAudioFile API, the other the AC and AF APIs
directly (what the ExtAF does "under the hood"). I think this is a
good starting point.
Bill
On 03/01/2006, at 11:54 AM, James McCartney wrote:
On Jan 3, 2006, at 12:59 AM, Alexander von Below wrote:
Hello,
while I am a true believer in RTFM, I am taking the liberty to ask
in this list if reading the CoreAudio docs will yield the desired
result ;)
What we want to do is to convert as many audio formats as possible
(well, mainly mp3, aac and Apple lossless) into canonical PCM.
Another requirement is compatibility from 10.2.8 to 10.4 (Universal).
On first sight, it looks like Core Audio could fulfill all of
these requirements. However, I was unable to find any MP3, AAC or
similar codecs in the filesystem - I might have been looking for
the wrong things, though.
So, is CoreAudio what I need? Or should I look for other options?
There are several levels at which you can do this. At the lowest
level is to call the AudioConverter and AudioFile APIs. This will
be compatible back to 10.2.8 for decoding mp3, aac, and lossless
(assuming a QuickTime with which lossless was shipped has been
installed). The AudioConverter can decode any format for which
codecs are installed in the system. AudioFile does the file parsing
and data handling.
For 10.4 you have more options. You can use the ExtAudioFile API
which is a easier to use wrapper for the AudioConverter and
AudioFile APIs.
And at the highest level if you don't need direct control, your app
could spawn the command line tool "afconvert" which can do about
everything ExtAudioFile can do.
afconvert is found in /Developer/Examples/CoreAudio/Services/
AudioFileTools.
Another related question is if anyone here knows if it is possible
at all to read AAC Protected (iTMS) files. I am aware that this
would first and foremost require an agreement with Apple, but if
there is the known chance of reaching such an agreement, we would
like to try.
If there is not even a remote chance to get such permission for
any company, then there is no reason in persuing this. I am a
aware of not-quite-so-legal ways of doing this, but that is not an
option. If we can not do it with Apple's blessing, then we just
won't.
The CoreAudio APIs do not provide a way to read protected files.
-- james mccartney -- apple coreaudio
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