Re: SR conversion and AUHAL
Re: SR conversion and AUHAL
- Subject: Re: SR conversion and AUHAL
- From: Philippe BERNERY <email@hidden>
- Date: Thu, 08 Dec 2005 16:58:27 +0100
Bjorn Roche wrote:
Hey CoreAudio folks,
I've been squinting at code and docs for a long time here, so sorry
if I am missing something obvious. Anyway, I understand from here:
http://developer.apple.com/technotes/tn2002/tn2091.html#FORMATS
that AUHAL does NOT provide sample rate conversion when doing input. I
think I saw a mailing list posting to that effect as well.
However, the PDFs on CoreAudio state:
An application can use an AudioOutputUnit to interface to a device. The
DefaultOutputAudioUnit tracks the selection of a device by the user as
the default output for audio, and provides additional services such as
sample rate conversion, to provide a simpler means of interfacing to an
output device.
So my conclusion was: "AudioOutputUnit does SR conversion for output,
but not input, so I will need to take care of input SR conversion myself
using an AudioConverter"
All well and good, but when I tried, I noticed I always had buffer
under/over-runs, so I skipped the conversion and everything seems to
work fine, and I get the same number of frames in and out over the long
run. It's entirely possible that I am not setting the sample rates
correctly, or something else dumb, but I'd like to clarify:
When, if ever, do I need to do SR conversion when using AUHAL?
TIA,
bjorn
-------------
Bjorn Roche
Check out my CD Mastering Software
for Mac OS X : http://www.xowave.com
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Actually AUHAL can only do "simple" conversion on input data. I try to
get input conversion works on Wengophone (http://dev.openwengo.com) and
I did it. Have a look at
http://dev.openwengo.com/trac/openwengo/trac.cgi/file/trunk/wifo/eXosip/phapi/phmedia-coreaudio.c
Functions are called this way:
- ca_open
- ca_start
- ca_close
You can see that I'm not using AUHAL for input but only a simple audio
device. Maybe you could find something with my code to get input
conversion works on portaudio with AUHAL.
--
Philippe BERNERY <email@hidden>
http://dev.openwengo.com
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