Re: My AUHAL Output Audio Unit
Re: My AUHAL Output Audio Unit
- Subject: Re: My AUHAL Output Audio Unit
- From: William Stewart <email@hidden>
- Date: Fri, 25 Jun 2004 11:09:37 -0700
The settings in the for loop are to -1 (that tells the underlying
converter in the AUHAL that those channels are not used).
Then following that you describe which channels of the device go into
the channels that you will receive...
In the example below you allocate a channel map that is as big as the
number of channels you *get* from the device, set them first to -1,
then after you describe for each channel of what you receive, which
channel of the device you want.
Thus, you are saying below that the first channel that you get, it will
be the channel 2 of the device... The second channel you receive will
be the channel 3 of the device.
Bill
On 24/06/2004, at 11:29 PM, Daniel Todd Currie wrote:
>
I've just finished implementing my AUHAL Output Audio Unit according
>
to the sample code and docs available here:
>
>
http://developer.apple.com/technotes/tn2002/tn2091.html
>
>
I run it and look at the buffer data that comes pouring into my app
>
and it is just a big long list of zeros. :(
>
>
I have no idea where to begin troubleshooting, as the AU setup sample
>
code seems pretty thorough and I have checked for all of the
>
ComponentResult errors in my AudioUnitSetProperty calls. I was a bit
>
perplexed by one of the listings in the link above, so I wonder if it
>
could be the problem. The block of code from that page:
>
>
> SInt32 *channelMap =NULL;
>
> UInt32 numOfChannels = DesiredFormat.mChannelsPerFrame; //2 channels
>
> UInt32 mapSize = numOfChannels *sizeof(SInt32);
>
> channelMap = (SInt32 *)malloc(size);
>
>
>
> //for each channel of desired input, map the channel from
>
> //the device's output channel.
>
> for(UInt32 i=0;i<numOfChannels;i++)
>
> {
>
> channelMap[i]=-1;
>
> }
>
> //channelMap[desiredInputChannel] = deviceOutputChannel;
>
> channelMap[0] = 2;
>
> channelMap[1] = 3;
>
> AudioUnitSetProperty(InputUnit, kAudioOutputUnitProperty_ChannelMap,
>
> kAudioUnitScope_Output, 1, channelMap, size);
>
>
Aside from what seems like a typo where "size" is used instead of
>
"mapSize", I don't understand why channelMap elements are set once in
>
the for loop, and then once again after the for loop. I implemented
>
the AU for my own needs as best I could from this example, but it
>
makes sense that if I were somehow mapping the channels incorrectly I
>
might get a bunch of silence. Can anyone shed a little light on the
>
snippet above?
>
>
Thanks a million,
>
>
-- Daniel Todd Currie
>
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