Re: support for two's complement 24 bit audio
Re: support for two's complement 24 bit audio
- Subject: Re: support for two's complement 24 bit audio
- From: Jeff Moore <email@hidden>
- Date: Tue, 30 Sep 2008 14:01:50 -0700
In CoreAudio, we use the AudioStreamBasicDescription structure to
describe a data format. This fields of this structure allow for the
precise description of all sorts of data formats. In particular for
linear PCM, the fields allow for describing pretty much any bit depth/
packing/number of channels you can think of.
In my talk at WWDC this year (and last year for that matter), I
covered this structure and how Core Audio uses it to describe various
kinds of audio formats. If you haven't already done so, you might want
to sign up for an ADC membership so you can get access to the
recordings of these talks.
On Sep 30, 2008, at 1:44 PM, Tommy Schell wrote:
Sorry I missed the reply to this question earlier.
So in the Quicktime specs, for audio data there is a reference to
the 4cc's:
'twos' for 16 bit two's complement big endian
'sowt' for 16 bit two's complement little endian
'in24' for 24 bit integer format
among others.
Elsewhere we have seen reference to the 'lpcm' format, which we
assume is what is used for
24 bit two's complement uncompressed audio data (big endian), not 1
of the above mentioned formats.
Is this a correct assumption?
Thanks a lot
Tommy Schell
********************
Message: 8
Date: Wed, 24 Sep 2008 10:30:37 -0700
From: William Stewart <email@hidden>
Subject: Re: support for two's complement 24 bit audio
To: CoreAudio API <email@hidden>
Message-ID: <email@hidden>
Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes
On Sep 23, 2008, at 7:13 PM, Jeff Moore wrote:
Two's complement is just another way of saying signed linear PCM,
isn't it?
So, I think we are understanding your question, and yes, core audio's
audio converter supports 24 bit (what we call signed) int formats:
We do support 8-bit (signed and unsigned), 16-, 24- and 32-bit
(signed) integer formats. (if not packed, high-aligned only)
For this the 24bit format is supported both as packed and as high-
aligned within a 32bit word
Bill
Begin forwarded message:
From: Tommy Schell <email@hidden>
Date: September 23, 2008 7:47:40 AM PDT
To: email@hidden
Subject: support for two's complement 24 bit audio
Hi,
I posted this question on the Quicktime list, but perhaps it is
more appropriate here.
Does support exist for 24 bit two's complement audio in Quicktime
files?
I found that 16 bit support is available for two's complement,
but I can't find it for 24
(or even extended to 32 bit) two's complement.
Can you please advise, and if it does not exist what might you
recommend to convert the two's complement
to a supported audio format in 24 bit?
Thanks a lot,
Tommy Schell
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--
Jeff Moore
Core Audio
Apple
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