Re: MOTU Format
Re: MOTU Format
- Subject: Re: MOTU Format
- From: Brad Ford <email@hidden>
- Date: Wed, 8 Dec 2004 21:34:52 -0800
On Dec 8, 2004, at 8:38 PM, Dominic Feira wrote:
Hello.
Could somebody explain the following AudioStreamBasicDescription to
me? This is from a MOTU 828 mkii.
- - - - - - - - - - - - - - - - - - - -
Sample Rate:48000.000000
Format ID:lpcm
Format Flags:2B
Bytes per Packet:4
Frames per Packet:1
Bytes per Frame:4
Channels per Frame:22
Bits per Channel:32
- - - - - - - - - - - - - - - - - - - -
I don't understand how there can be 22 Channels per Frame, but yet
there are only 4 Bytes per Frame.
Format Flags 2B =
kAudioFormatFlagIsFloat +
kAudioFormatFlagIsBigEndian +
kAudioFormatFlagIsPacked +
kAudioFormatFlagIsNonInterleaved
(non interleaved is the important one). To quote from CoreAudioTypes.h:
However, when an ASBD has the kAudioFormatFlagIsNonInterleaved flag,
the
AudioBufferList has a different structure and
semantic. In this case, the ASBD
fields will describe the format of ONE of the
AudioBuffers that are contained in
the list, AND each AudioBuffer in the list is
determined to have a single (mono)
channel of audio data. Then, the ASBD's
mChannelsPerFrame will indicate the
total number of AudioBuffers that are contained
within the AudioBufferList -
where each buffer contains one channel.
So when non-interleaved flag is set, the rest of the fields in the asbd
describe just 1 of the buffers. There will be 22 buffers that all have
this format.
HTH
-Brad Ford
QuickTime Engineering
Dominic Feira / Code Monkey / Ambrosia Software, Inc.
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| | >MOTU Format (From: Dominic Feira <email@hidden>) |