Re: alcCaptureSamples crashes on stereo capturing

On 2012-08-10 05:20:44 +0200, Chris Robinson said:

> On 08/09/2012 07:14 AM, Philipp Kraus wrote:
>> Hello,
>> 
>> I have got this code for capturing mono 8 bit data, the code works
>> without any error:
>> 
>> m_device = alcCaptureOpenDevice( p_device.c_str(),
>> static_cast<ALCuint>(p_sampingfrequency),  AL_FORMAT_MONO8,
>> static_cast<ALCsizei>(p_buffersize));
>> 
>> ublas::vector<ALubyte> l_buffer(m_buffersize);
>> alcCaptureStart(m_device);
>> while(m_capturing)
>> {
>> alcGetIntegerv(...)
>> l_samplesread = std::min(
>> static_cast<std::size_t>(l_samplesread), l_buffer.size()-i);
>> alcCaptureSamples(m_device, (ALCvoid*)(&l_buffer[i]),
>> l_samplesread);
>> }
>> 
>> If I switch the the AL_FORMAT_MONO8 to AL_FORMAT_STEREO8 and change the
>> p_buffersize to 2*p_buffersize & m_buffersize to 2*m_buffersize the code
>> crashes
>> on the alcCaptureSamples line and the buffer is not filled.
> 
> It looks like you're not accounting for the count being in sample 
> frames, so you're asking for n sample frames, but only have enough 
> space for n/2 (since it needs two channels for each sample frame). 
> l_buffer.size() is samples*channels, not the number of samples.
> 
> l_buffer.size()/2 is the number of samples to fill for stereo.

Yes, my code shows exactly;


m_device = alcCaptureOpenDevice( p_device.c_str(),  
static_cast<ALCuint>(m_samplingfrequency),  AL_FORMAT_STEREO8,   
static_cast<ALCsizei>(m_buffersize));
ublas::vector<ALubyte> l_buffer(2*m_buffersize);
alcCaptureStart
wile(m_capturing)
    {
        for(std::size_t i=0; i < l_buffer.size(); )
        {
            ALint l_samplesread = 0;
            alcGetIntegerv(m_device, ALC_CAPTURE_SAMPLES, 
static_cast<ALCsizei>(sizeof(ALint)), &l_samplesread);
 i	  if ( (!l_samplesread) && (alcIsExtensionPresent(m_device, 
"ALC_EXT_disconnect")) )
            {
                    stop capturing
            }

            if (l_samplesread > 0)
            {
                l_samplesread = std::min( 
static_cast<std::size_t>(l_samplesread), l_buffer.size()-i);
                alcCaptureSamples(m_device, (ALCvoid*)(&l_buffer(i)), 
l_samplesread);
                i += l_samplesread;
            }
        }
}
alcCaptureStop

I think this correct, because the buffer has got the double size, so 
left / right channel are correct stored. If I write the l_buffer down 
to std::cout the values are correct, but
on calling the dtor of my object, I get the same error.
My l_samples is the number of samples that are read or is it on stereo 
the number of frames?
IMHO a frame stores 2 elements of ALubyte, so my buffer must have 
2*m_buffersize

Thanks

Phil 


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