[Openal] AL_FORMAT Types and Meanings

[Daniel PEACOCK]

Hi Ümit,

What is your goal with this algorithm?   Are you trying to extract
particular channels from a wavefile, or are you attempting to mix several
channels into one or more channels (downmixing)?

>> I mean for example we have 16 bit sampled 5.1 sound which will be played
only front left

e..g. Does this mean you want to hear the front-left channel only (and
remove the other 5 channels of data), or do you want to mix all 6 channels
together into a mono file?

Dan
Creative Labs (UK) Ltd.

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             Ümit Uzun                                                     
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                                       [Openal] AL_FORMAT Types and        
             10/01/2009 02:17          Meanings                            
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Hi All,

I have needed to control every channel manually so I have injected
Framework.cpp of OpenAL SDK.
I added

template<typename T> T *LoadData(const T *data, int size, const char
*channels, short channelType)
{     size /= sizeof(T);      T *multData = new T[size * channelType];  
for(int i = 0; i < size; i++)     {         for(int k = 0; k < channelType;
k++)         {             multData[i * channelType + k] = channels[k] == '1'
? data[i] : 0;         }     }      return multData;
}

const char *channels; // For example 110010
// Find channelType by counting channels value for example 5.1's
channelType == 6
short channelType;
for(channelType = 0; channels[channelType] != NULL; channelType++);
if(fmt.wBitsPerSample == 16)   // assumes 16-bit short
{     ALshort *data = LoadData((const ALshort*)pData, iDataSize, channels,
channelType);     switch(channelType)     {     case 2: 
alBufferData(uiBufferID, alGetEnumValue("AL_FORMAT_MONO16"), data,
iDataSize * channelType, iFrequency);     break;     case 4: 
alBufferData(uiBufferID, alGetEnumValue("AL_FORMAT_QUAD16"), data,
iDataSize * channelType, iFrequency);     break;     case 6: 
alBufferData(uiBufferID, alGetEnumValue("AL_FORMAT_51CHN16"), data,
iDataSize * channelType, iFrequency);     break;     case 7: 
alBufferData(uiBufferID, alGetEnumValue("AL_FORMAT_61CHN16"), data,
iDataSize * channelType, iFrequency);     break;     case 8: 
alBufferData(uiBufferID, alGetEnumValue("AL_FORMAT_71CHN16"), data,
iDataSize * channelType, iFrequency);     break;     }     delete[] data;
}

instead of
alBufferData(uiBufferID, eBufferFormat, pData, iDataSize, iFrequency);
command.

With this changing I can specify each channel for related buffer's will be
played.
I specify each sounds channel value by;
<!-- Channels Enum for 5.1 123456   -->
<!--   1 : Front Left      Speaker  -->
<!--   2 : Front Right     Speaker  -->
<!--   3 : Front Center    Speaker  -->
<!--   4 : Low   Frequency Speaker  -->
<!--   5 : Back  Left      Speaker  -->
<!--   6 : Back  Right     Speaker  -->

In LoadData template function I create the multData sound buffer data in
this sequence. I mean for example we have 16 bit sampled 5.1 sound which
will be played only front left(this sound's channels:100000) I send the raw
pData sound buffer to LoadData function and multiplex this sound data for 6
channel in given sequence order. Create new multData array for 6 channel
and start to set this sound array firstly Front Left and Front Right and so
on.
So do you think this operation right or now?

With all those changing I want to control channels. Because I have some
sounds which only must played on rear left channel and some sounds only
front right and etc.
Do you think this approach is suitable?

And another question I want to handle 2.0 speaker like 5.1 and as you can
see I use AL_FORMAT_MONO16 for 2 channel. Do you think it's right or not?
Should I use AL_FORMAT_STEREO16? Or which enumeration do I need?

If I am so complex, please ask me question to lead you right direction.
Regards.

Ümit Uzun_______________________________________________
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