Re: AudioStreams
Re: AudioStreams
- Subject: Re: AudioStreams
- From: Michael Thornburgh <email@hidden>
- Date: Sun, 17 Nov 2002 17:02:25 -0800
hi greg.
i believe the best description of what a stream is, in this context,
can be found in the AudioHardware.h header file in
/System/Library/Frameworks/CoreAudio.framework/Headers/:
// An Audio Device is further broken down into Audio Streams. An
Audio Stream
// encapsulates the buffer of memory for transferring the audio
data across
// the user/kernel boundary. Like Audio Devices, the Audio Stream
provides
// properties that describe and control it. Audio Streams always
have a single
// direction, either input or output.
there's more about streams in there, too.
the idea is an audio device's actual IO is composed of zero or
more streams for each direction. a stream is a collection of
channels plus their control information, like per-channel volume
settings, format, etc. further, an AudioStream _should_ mimic
how the IO with the device actually works. imagine a theoretical
device with 3 stereo output jacks. this could be represented as three
2-channel streams in the output direction. and perhaps each
stream's physical format could be set independently (first one
8-bit, 2nd one 16-bit, etc). (the presentation to your IOProc
would be as Float32s of course)
i hope this helps. :)
AudioHardware.h has a very good description of the Whole Idea of the
HAL.
definitely read the whole "Theory of Operation" section, if you haven't
already, as all of those ideas apply to MTCoreAudio as well.
-mike
On Sunday, November 17, 2002, at 04:06 PM, Greg Hamilton wrote:
Hi,
I've written an app to record / playback using CoreAudio and
MTCoreAudio. It's pretty simple, just an MTCoreAudioDevice object for
record and another for playback, each with it's own ioProc for reading
/ writing data.
I've read both the quite old coreaudio.pdf from Apple
(http://developer.apple.com/audio/pdf/coreaudio.pdf) and the
MTCoreAudio docs. Both make mention of AudioStreams and the
MTCoreAudio framework even provides two Objective C classes as
wrappers for AudioStreams and AudioStreamDescriptions but neither
documents explain exactly what AudioStreams are for nor how to use
them so I'm left making guesses based on the methods available in the
MTCoreAudioStream class.
What are AudioStreams and why would I use them ?
Greg
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| References: | |
| | >AudioStreams (From: Greg Hamilton <email@hidden>) |