OpenAL

Hi all,

my name is Angelo and i am quite new to OpenAl/audio world.
I need some suggestions and help for a task.
I have to develop a portable software on a pc side, that mainly
have to playback a PCM 16bit samples, 8Khz, LSB(Little endian
Intel format) mono samples. The stream contain pure audio
vocal samples, no high quality is required.
Actually, i am working under windows since this is the main
request for the project.

The stream is generated from a little 80186 based device that i
am writing the firmware for it, planning to send packets of
512/1024 bytes, constant bitrate, 1 packet about every 30
msec.

So, mi questions would be:
- i am using format = AL_FORMAT_MONO16, does it match the
incoming stream ? I think it should.
- is the streaming timing interval of 30msec and packet size
512 or 1024 correct for this purpose ?
- could anyone suggest me some little sample that show how
queue/unqueue the buffers and play them in the correct way ?

infinite thanks,
Angelo

Hi, Angelo.
A packet size of 1024 bytes of 16-bit mono data would yield
512 samples. For 8khz, 512 samples is roughly 63ms. This
should be adequate for a send inverval of 30ms, as long as
you don't have much packet loss. A packet size of 512 bytes
would be half that, giving 256 samples, for a length of 31ms,
which would be cutting it close.

I'm not too familiar with the networking side of things, but the
queueing/unqueueing could work like this:

ALint processed;
ALint state;
alGetSourcei(source, AL_SOURCE_STATE, &state);
alGetSourcei(source, AL_BUFFERS_PROCESSED, &processed);
while(alGetError() != AL_NO_ERROR && processed > 0) {
    ALubyte *data;
    ALuint buf;
    int length;

    data = get_packet_data(&length);
    if(!data) break;

    alSourceUnqueueBuffers(source, 1, &buf);
    if(alGetError() == AL_NO_ERROR) {
        alBufferData(buf, AL_FORMAT_MONO16, data, length,
                     8000);
        alSourceQueueBuffers(source, 1, &buf);
    }
    processed--;
}

if(state != AL_PLAYING)
    alSourcePlay(source);

Hope that helps. :)