This example opens separate OSS capture and playback channels in mmap mode, places them into a sync group, and starts them together so both ring buffers advance on the same device timeline. It then monitors the capture mmap pointer with SNDCTL_DSP_GETIPTR, converts that pointer into monotonic absolute progress using the reported block count, and copies newly recorded audio from the input ring to the matching region of the output ring.
The main loop is driven by an absolute monotonic frame clock rather than a fixed relative usleep delay. Wakeups are scheduled from the sample rate using a small frame step similar to the SOSSO timing model, while the audio path itself stays intentionally simple: just copy input to output, with no explicit xrun recovery or processing beyond ring wraparound handling.