Restarting Streaming OpenAL Source? - c++

Question

Why does my streaming OpenAL source somtimes go to AL_STOPPED state, forcing me to call alSourcePlay? This usually happens when I do not call send fast enough, i.e. in debug mode. Does the oal source automatically stop when it doesn't have enough queue buffers? How do I avoid that?
void send(audio_buffer audio) override
{
ALenum state;
alGetSourcei(source_, AL_SOURCE_STATE,&state);
if(state != AL_PLAYING)
alSourcePlay(source_); // This happens sometimes, usually when "send" is not called fast enough.
ALuint buffer = 0;
alSourceUnqueueBuffers(source_, 1, &buffer);
if(buffer)
{
alBufferData(buffer, AL_FORMAT_STEREO16, audio.data(), static_cast<ALsizei>(audio.size()*sizeof(int16_t)), 48000);
alSourceQueueBuffers(source_, 1, &buffer);
}
else
LOG << "Dropped audio.";
}

Answer 1

It sounds like your basic problem is that your audio stream is starved. There are a few options you can use to mitigate this, but they all have their own side effects:
(1) You can configure it to play from a looping buffer, to which you are supplying the relevant data. The downside to this is that it will audibly repeat itself if you starve the buffer too long, but it will have some better performance characteristics (fragmentation, etc).
(2) You can increase the send buffer size. This will only cover up small problems, and potentially increases the latency in dynamic content.
(3) Finally, you can thread the audio send operation, that way so long as the audio thread isn't starved, it can continue to send data in the background.
The high production / quality solution probably involes all three of these. Sorry for the lack of OpenAL specific terminology, but every audio system I've seen has these capabilities.