Re: how do I change bitsperchannel value
Re: how do I change bitsperchannel value
- Subject: Re: how do I change bitsperchannel value
- From: "apple question" <email@hidden>
- Date: Mon, 10 Jul 2006 13:54:04 -0800
Ok. In my original program I am getting the mFormatFlags value from iSight,
which is kAudioFormatFlagIsFloat | kAudioFormatFlagIsPacked. When I try to
change bitsperchannel from 32 to 16 without changing the flag, create
converter fails. Now if I change the new 16bit flag to
kLinearPCMFormatFlagIsSignedInteger , it will pass. So the idea seems to be
for kAudioFormatFlagIsFloat to set, the bitsperchannel value should be
muliple of 4 bytes. Thanks Doug and Geoff for their help.
From: Doug Wyatt <email@hidden>
To: apple question <email@hidden>
CC: email@hidden
Subject: Re: how do I change bitsperchannel value
Date: Mon, 10 Jul 2006 14:18:35 -0700
On Jul 10, 2006, at 14:04 , apple question wrote:
I am using the following test function. Any idea what is wrong here? Are
we even allowed to do simple bitsperchannel converting? Thanks.
OSStatus Test::TestConverter()
{
OSStatus err;
AudioConverterRef converter;
int nChannels = 1;
CAStreamBasicDescription inDataFormat;
inDataFormat.mFormatID = kAudioFormatLinearPCM;
inDataFormat.mFormatFlags = kLinearPCMFormatFlagIsSignedInteger |
kAudioFormatFlagIsPacked; //Little Endian
inDataFormat.mBytesPerPacket = inDataFormat.mBytesPerFrame = nChannels *
2;
for 32 bits this should be nChannels * 4
inDataFormat.mFramesPerPacket = 1;
inDataFormat.mChannelsPerFrame = nChannels;
inDataFormat.mBitsPerChannel = 32;
CAStreamBasicDescription outDataFormat = inDataFormat;
outDataFormat.mBitsPerChannel = 16;
for 16 bits this should be nChannels * 2
More generally, you could set mBitsPerChannel first (as long as it's an
even multiple of 8), then:
mBytesPerPacket = mBytesPerFrame = nChannels * mBitsPerChannel / 8;
err = AudioConverterNew(&inDataFormat, &outDataFormat, &converter);
//fail, errcode "fmt?"
return err;
}
Then this will work.
Doug
--
Doug Wyatt
Core Audio, Apple
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