Re: AAC recording issues

Subject: Re: AAC recording issues
From: Jaime Magiera <email@hidden>
Date: Thu, 29 Nov 2007 16:04:59 -0500

On Nov 29, 2007, at 2:33 PM, Eric Allamanche wrote:

Jaime,

the supported AAC bit rate ranges for given sample rates are the following:

22050, 24000 Hz: 16000 to 64000 bps
32000 Hz: 24000 to 96000 bps
44100, 48000 Hz: 32000 to 160000 bps

These rates are per channel bit rates so you'll have to double them for stereo signals. Please verify that your parameters match these ranges.

Hi, thanks for the response. I think they are set properly. For example, I've just now done a test hardcoding the parameters below. However, I end up with a empty 4k file using either my line-in or iChat mic (MBP). Thanks for any help.

Jaime

Settings...

dataFormat.mSampleRate = 48000;

dataFormat.mFormatID = kAudioFormatMPEG4AAC;

dataFormat.mFormatFlags = 0;

dataFormat.mChannelsPerFrame = 2;

dataFormat.mFramesPerPacket = 1024;

dataFormat.mBitsPerChannel = 0;

dataFormat.mBytesPerPacket = dataFormat.mBytesPerFrame = 0;

bitrate = (UInt32)64000;

...

recfile.SetConverterProperty(kAudioConverterEncodeBitRate, sizeof(UInt32), &bitrate);

I even iterate through the device variables to be sure it's supported...

2007-11-29 16:01:57.435 myApp[3978:813] The volume of the device before recording 0.521739

2007-11-29 16:01:57.437 myApp[3978:813] the selected sampling rate: 48000

2007-11-29 16:01:57.438 myApp[3978:813] the selected channels: 2

2007-11-29 16:01:57.438 myApp[3978:813] Nominal Sampling rates from device (

(

44100,

44100

(

48000,

48000

(

96000,

96000

)

2007-11-29 16:01:57.473 myApp[3978:813] Minimum 8000.000000, Maximum 8000.000000 and desired 64000

2007-11-29 16:01:57.473 myApp[3978:813] Minimum 12000.000000, Maximum 12000.000000 and desired 64000

2007-11-29 16:01:57.473 myApp[3978:813] Minimum 16000.000000, Maximum 16000.000000 and desired 64000

2007-11-29 16:01:57.474 myApp[3978:813] Minimum 20000.000000, Maximum 20000.000000 and desired 64000

2007-11-29 16:01:57.474 myApp[3978:813] Minimum 24000.000000, Maximum 24000.000000 and desired 64000

2007-11-29 16:01:57.475 myApp[3978:813] Minimum 28000.000000, Maximum 28000.000000 and desired 64000

2007-11-29 16:01:57.475 myApp[3978:813] Minimum 32000.000000, Maximum 32000.000000 and desired 64000

2007-11-29 16:01:57.475 myApp[3978:813] Minimum 40000.000000, Maximum 40000.000000 and desired 64000

2007-11-29 16:01:57.476 myApp[3978:813] Minimum 48000.000000, Maximum 48000.000000 and desired 64000

2007-11-29 16:01:57.476 myApp[3978:813] Minimum 56000.000000, Maximum 56000.000000 and desired 64000

2007-11-29 16:01:57.476 myApp[3978:813] Minimum 64000.000000, Maximum 64000.000000 and desired 64000

2007-11-29 16:01:57.477 myApp[3978:813] Minimum 72000.000000, Maximum 72000.000000 and desired 64000

2007-11-29 16:01:57.480 myApp[3978:813] Set bitrate

2007-11-29 16:02:05.903 myApp[3978:813] Stop Recoding

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References:
	>AAC recording issues (From: Jaime Magiera <email@hidden>)
	>Re: AAC recording issues (From: Eric Allamanche <email@hidden>)

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