Accessing AudioCodec from AudioConverter?
Accessing AudioCodec from AudioConverter?
- Subject: Accessing AudioCodec from AudioConverter?
- From: "Stephen F. Booth" <email@hidden>
- Date: Tue, 27 Dec 2005 09:21:17 -0800
Hello all,
I am new to Core Audio programming and am stuck! In essence, I want
to set the options for the codec used by an AudioConverter;
specifically I want to set the bitrate mode (CBR, ABR, VBR) on the
AAC codec. Setting the kAudioConverterSampleRateConverterQuality
property does not seem to do the trick. I am aware of the
kAudioConverterPropertyInputCodecParameters /
kAudioConverterPropertyOutputCodecParameters properties, but I cannot
find any documentation on how to use them. I have also looked into
the kAudioFormatProperty_FormatIsVBR property on
AudioStreamBasicDescription, but this seems informational only.
"AudioCodec.h" defines the following
// constants to be used with kAudioCodecBitRateFormat
enum
{
kAudioCodecBitRateFormat_CBR = 0, // Every encoded frame is the
same size
// eg IMA, MACE, old MP3, most early audio codecs
kAudioCodecBitRateFormat_ABR = 1, // Encoder attempts to keep close
to the given bit rate, can vary
// eg modern MP3 CBR, AAC (anything that has a "minimum"
frame size
// or implements a bit pool for "CBR")
kAudioCodecBitRateFormat_VBR = 2 // Encoder varies frames size
attempting to maintain constant quality
// eg MP3 VBR (Xing), AAC VBR
};
but I cannot find a way to access the AudioCodec (which I presume is
used internally by AudioConverter) directly.
Could anyone shed some light on this matter?
Stephen
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