Re: AudioDevice vs. AudioUnit
Re: AudioDevice vs. AudioUnit
- Subject: Re: AudioDevice vs. AudioUnit
- From: Jeff Moore <email@hidden>
- Date: Tue, 15 Apr 2003 12:21:53 -0700
Except for special cases, I would say that for output, you are best off
using the Output Audio Unit rather than directly using the HAL
yourself. The AU will do a lot of the busy work that a proper HAL
client has to implement for you. Plus, it use an AudioConverter
internally to massage the incoming data into the format the hardware
wants.
On Monday, April 14, 2003, at 07:36 PM, Steven A. Kortze wrote:
This might seem to be a rather rudimentary question, but I was
curious. I have seen several selections of source code that use the
AudioDevice (AudioHardware API or Hardware Abstraction Layer -- a.k.a.
HAL) for basic CoreAudio support. One example is the mpg123 port for
OS X. This seems fine if the assumption made for that sample code is
valid. The assumption is that the user will be using 2-channel
hardware via the built-in audio hardware. If the user is using an
8-channel sound card, such as the M-Audio Revolution PCI card, the
assumption is no longer valid. On the other hand, the developer may be
using AudioDevices to minimize any overhead in processing the sound
and to use the lowest API that he can.
To properly handle both of these cases, the developer would need to
use the AudioUnit API. Is that statement correct? In this manner, the
developer could set up source and destination formats and allow for
any 2 to 8 channel conversion or any other conversions that might be
necessary. What kind of performance degradation can occur by putting
these conversions into the audio stream? For example, suppose that I
want to decode some MP3 files and play the sound back via the
8-channel Revolution hardware. Is the 2-to-8 channel conversion a
significant one? Would AudioUnits be the best approach in this case?
Thank you,
Steve
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--
Jeff Moore
Core Audio
Apple
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