Re: AAC encoder - what codec or converter setting to encode to Mono?
Re: AAC encoder - what codec or converter setting to encode to Mono?
- Subject: Re: AAC encoder - what codec or converter setting to encode to Mono?
- From: Brad Ford <email@hidden>
- Date: Tue, 11 Jul 2006 16:36:25 -0700
On Jul 11, 2006, at 4:17 PM, Simon Liu wrote:
OS X 10.4. 7 - I can encode Linear PCM to AAC using
AudioConverterFillComplexBuffer(), but I have been unable to set the
converter/codec settings to encode from LPCM Stereo to AAC Mono
(ideally downmixed).
AudioConverter does not do mixing. It can duplicate, drop, or
reorder source channels, but cannot mix them. If you need to do a
mix, you can set up a MatrixMixer AudioUnit ahead of the
AudioConverter to do the stereo->mono mix.
-Brad Ford
QuickTime Engineering
My three attempts so far:
1. Changed the converter's destination ASBD mChannelsPerFrame per
frame to 1 does not work, as the converter does not init and returns
'?tmf'
2. I found the audio converter property
kAudioCodecPropertyOutputChannelLayout, but it is not writable.
3. I tried settingthe property kAudioConverterChannelMap with a
channel map of:
SInt32 channelMap[1] = { 0 };
I thought the converter would encode using audio from the first
channel, and ignore the second input channel. In fact, nothing
happened, and the resulting M4A was in stereo.
When I get the converter properties, I also see the following:
key = "Channel Configuration";
"limited values" = (Stereo);
So it seems the converters' other settings may be preventing me from
choosing Mono as the channel configuration.
Can anybody help? Thank you.
Regards,
Simon
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