Re: best way to get rate conversion
Re: best way to get rate conversion
- Subject: Re: best way to get rate conversion
- From: Bill Stewart <email@hidden>
- Date: Fri, 11 Oct 2002 16:15:05 -0700
Phil
on 10/10/02 6:21 PM, Phil Burk wrote:
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Thanks for the info.
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I've been playing with the examples "UsingAudioConverter.cpp" and
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"UsingDefaultNoAC.cpp". This has raised some questions.
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1) I found the headers on disk, and the "Audio and MIDI on Mac OS X (pdf)"
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doc at
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http://developer.apple.com/audio/macosxaudio.html.
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But I can't find any detailed references to the functions like
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AudioConverterFillBuffer(). Can you give me a link to the online reference
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docs?
We still have to do this - I'm finishing up some revs to the AU docs that we
hope to release soon. The AC is next on the list
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2) I tried to download the latest CoreAudio SDK (9/7/2002) but it won't
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install. Does it need Jaguar?
Yes
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3) The PDF doc says "kAudioUnitID_DefaultOutput. This is a specialized HAL
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output unit that provides additional services, such as sample rate
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conversion,". Does this mean that if I want to use arbitrary devices, not
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the "default" device that I need to use kAudioUnitID_HALOutput and it does
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not support rate conversion. So I need to use an AudioConverter?
That's out of date...
In Jaguar there is a AUConverter unit that wraps up the converter and will
do bit-depth, SRC, channel interleaving/deinterleaving
ALL of the output units inherit from AUConverter, so they will all do this
work for you - you just specify the input format of these units, then it
will give you a buffer for that format
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4) Can I use an AudioConverter with the HAL and not have to use an
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AudioOutputUnit? I've already got the HAL working except for SR conversion.
Sure - you can also bypass the converter in the output units by making sure
your input format is the same as the output unit's output format (which will
be the device format)
We do this in some of our usage of this, and then run a graph say, at the
basic hardware format - so any conversion is just done on those inputs that
require it...
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5) What is the difference between AudioConverterFillBuffer() and
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AudioConverterConvertBuffer()? Is the latter for pushing data which I would
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need if I am converting audio input?
Convert can really only be used for bit depth type conversions. For SRC you
will need to do the FillBuffer. The FillComplexBuffer has a good match with
the AudioUnit V2 data structures
Have a look through the play-file implementation that is in the SDK
(PublicUtility)
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Thanks. Once I get tuned into the detailed SDK docs I won't ask so many
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questions...
No problems - once we get more docs done, you won't need to I hope:)
Bill
>
Phil Burk
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