This optional callback happens when the sound device runs out of
buffered audio data to play. After this occurs, the outstream waits
until the buffer is full to resume playback.
This is called from the SoundIoOutStream::write_callback thread context.
This optional callback happens when the sound device runs out of buffered audio data to play. After this occurs, the outstream waits until the buffer is full to resume playback. This is called from the SoundIoOutStream::write_callback thread context.