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Re: mFormatID != kAudioFormatLinearPCM
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Re: mFormatID != kAudioFormatLinearPCM


  • Subject: Re: mFormatID != kAudioFormatLinearPCM
  • From: Jeff Moore <email@hidden>
  • Date: Fri, 14 Mar 2003 19:12:03 -0800

The reason why iTunes does that is that it does not change the settings of the hardware. It will use whatever the hardware is currently set to. iTunes (and all Sound Manager clients for that matter) doesn't work with non-linear PCM devices.

Plus, iTunes only uses the default output device. The HAL specifically won't allow a device that doesn't have linear PCM as it's current format to be the default device.

On Friday, March 14, 2003, at 06:49 PM, Jon Lech Johansen wrote:

On Fri, Mar 14, 2003 at 05:45:40PM -0800, Jeff Moore (email@hidden) wrote:
I would consider the following statement true:
"If AudioDeviceGetProperty(kAudioDevicePropertyStreamFormat).mFormatID
!= kAudioFormatLinearPCM, the caller can safely assume that the device
does not support kAudioFormatLinearPCM currently."

You need to use kAudioDevicePropertyStreamFormats to get the list of
all the formats the stream supports.

Is not doing so considered a bug by Apple?

If the device supports kAudioFormatLinearPCM, but
AudioDeviceGetProperty(kAudioDevicePropertyStreamFormat).mFormatID !=
kAudioFormatLinearPCM, iTunes doesn't seem to check
kAudioDevicePropertyStreamFormats or use
kAudioStreamPropertyPhysicalFormatMatch, and the audio is instead sent
to the built-in audio device.

--
Jon Lech Johansen
email@hidden
nanocrew.net/blog/

Stat sua cuique dies, breve et inreparabile tempus
omnibus est vitae; sed famam extendere factis,
hoc virtutis opus.
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--

Jeff Moore
Core Audio
Apple
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