WASAPI output component version 3.0 final
Reply #133 –
"0" should use a default buffer size or some minimum. And no, it doesn't change jitter. Buffer size is a tradeoff between latency (doesn't matter in an audio player), memory usage, efficiency (larger buffers improve efficiency) and glitch prevention.
If you could set buffer sizes arbitrary low then you'd either experience massive glitches or no sound playing at all.