Brad,
Thanks for the fast response.
This isn't mixing. As you say, this just replicating the audio
data to multiple channels. This is what the channel map property
is for AFAIK.
Also, I seem to have just figured out the problem. I always figure
things out right after I hit send. Apparently AudioConverterReset
() throws out the channel map for some converters and not others.
I'm not sure what the defined behavior is supposed to be.
Thanks for the additional info though. I didn't realize that by
replicating the mono audio to both stereo channels that this was
considered too loud.
Dominic Feira / Code Monkey / Ambrosia Software, Inc.
On Nov 27, 2006, at 7:20 PM, Brad Ford wrote:
On Nov 27, 2006, at 4:13 PM, Dominic Feira wrote:
Can an AudioConverter decode AAC-mono to lpcm-stereo or Apple
Lossless-mono to lpcm-stereo?
No. AudioConverters don't mix.
I am able to decode *all* other audio formats to lpcm stereo
correctly by using a channel map.
I don't see how this could be true. If you're using a channel
map, you're likely replicating one channel of input to two
channels of output (and now the result is too loud), or dropping
one channel of input when going stereo->mono.
If you're going stereo->mono or mono->stereo, you really need to
perform a mix yourself, use a mixer audio unit, or use something
like QuickTime's SCAudio component, which has the same interface
as AudioConverterFillComplexBuffer (see SCAudioFillBuffer in
QuickTimeComponents.h), but _does_ perform a mix for you.
-Brad Ford
QuickTime Engineering
It seems as if the AAC and ALAC converters are not respecting the
channel map at all.
Setting the map on the AAC converter does not return an error.
While debugging this, I also ask the converter for the channel
map right after I set it and everything appears correct. Both
output channels are mapped to channel 0.
Thanks.
Dominic Feira / Code Monkey / Ambrosia Software, Inc.
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