feat: added full support in USB (local) & ethernet (local or remote) of audio for Icom

internal/audio/engine.go

@@ -5,6 +5,7 @@ package audio
 import (
 	"fmt"
 	"runtime"
+	"sync"
 	"time"
 	"unsafe"
 
@@ -269,3 +270,151 @@ func playPCM(deviceID string, pcm []byte, rate, ch, bits int, stop <-chan struct
 		time.Sleep(10 * time.Millisecond)
 	}
 }
+
+// pcmRing is a thread-safe, latency-bounded FIFO of PCM bytes feeding a live
+// render stream. Producers (a USB-codec capture, or a decoded network audio
+// stream) Push freshly-arrived samples; the render loop Pulls. It is the shared
+// hand-off point between "where the audio comes from" (USB device / UDP 50003)
+// and "where it's heard" (any WASAPI output) — so the transport can be swapped
+// without touching the render side, mirroring the civTransport split on the CAT
+// side. On overflow the oldest audio is dropped to keep latency bounded; on
+// underrun Pull simply returns short and the render loop pads with silence.
+type pcmRing struct {
+	mu  sync.Mutex
+	buf []byte
+	max int // hard cap in bytes (drops oldest beyond this → bounded latency)
+}
+
+// newPCMRing makes a ring whose backlog is capped at maxBytes. Size it from the
+// acceptable latency: bytesPerSec (=32000) worth ≈ 1 s.
+func newPCMRing(maxBytes int) *pcmRing {
+	if maxBytes <= 0 {
+		maxBytes = bytesPerSec // 1 s default
+	}
+	return &pcmRing{max: maxBytes}
+}
+
+// Push appends samples, dropping the oldest audio if the backlog would exceed
+// the cap (a slow/absent consumer never makes the producer block or grow without
+// bound). A short glitch beats runaway latency for live monitoring.
+func (r *pcmRing) Push(p []byte) {
+	if len(p) == 0 {
+		return
+	}
+	r.mu.Lock()
+	r.buf = append(r.buf, p...)
+	if len(r.buf) > r.max {
+		drop := len(r.buf) - r.max
+		r.buf = append(r.buf[:0], r.buf[drop:]...)
+	}
+	r.mu.Unlock()
+}
+
+// pull removes and returns up to maxBytes of queued PCM (a private copy), or nil
+// when empty. The render loop pads any shortfall with silence.
+func (r *pcmRing) pull(maxBytes int) []byte {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	if len(r.buf) == 0 || maxBytes <= 0 {
+		return nil
+	}
+	n := maxBytes
+	if n > len(r.buf) {
+		n = len(r.buf)
+	}
+	out := make([]byte, n)
+	copy(out, r.buf[:n])
+	r.buf = append(r.buf[:0], r.buf[n:]...)
+	return out
+}
+
+// renderStream continuously renders PCM pulled from src to a device until stop
+// closes — the streaming counterpart to playPCM's fixed buffer. On underrun it
+// writes silence rather than glitching, keeping the WASAPI clock steady so live
+// monitor audio flows smoothly even when the source stalls briefly. Runs on a
+// COM-initialised, OS-locked thread.
+func renderStream(deviceID string, rate, ch, bits int, stop <-chan struct{}, src *pcmRing) error {
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+	if err := coInit(); err != nil {
+		return fmt.Errorf("CoInitialize: %w", err)
+	}
+	defer ole.CoUninitialize()
+
+	dev, err := openDevice(wca.ERender, deviceID)
+	if err != nil {
+		return err
+	}
+	defer dev.Release()
+
+	var ac *wca.IAudioClient
+	if err := dev.Activate(wca.IID_IAudioClient, wca.CLSCTX_ALL, nil, &ac); err != nil {
+		return fmt.Errorf("activate render: %w", err)
+	}
+	defer ac.Release()
+
+	frameBytes := ch * bits / 8
+	if frameBytes <= 0 {
+		return fmt.Errorf("bad audio format")
+	}
+	wfx := &wca.WAVEFORMATEX{
+		WFormatTag: 1, NChannels: uint16(ch), NSamplesPerSec: uint32(rate),
+		NAvgBytesPerSec: uint32(rate * frameBytes), NBlockAlign: uint16(frameBytes),
+		WBitsPerSample: uint16(bits), CbSize: 0,
+	}
+	if err := ac.Initialize(wca.AUDCLNT_SHAREMODE_SHARED, autoConvert,
+		wca.REFERENCE_TIME(bufferDuration100ns), 0, wfx, nil); err != nil {
+		return fmt.Errorf("initialize render: %w", err)
+	}
+	var bufFrames uint32
+	if err := ac.GetBufferSize(&bufFrames); err != nil {
+		return err
+	}
+	var arc *wca.IAudioRenderClient
+	if err := ac.GetService(wca.IID_IAudioRenderClient, &arc); err != nil {
+		return fmt.Errorf("get render service: %w", err)
+	}
+	defer arc.Release()
+
+	// feed fills up to `frames` render frames: as much real audio as the ring
+	// has, the remainder silence (so the buffer stays full and the clock steady).
+	feed := func(frames int) error {
+		if frames <= 0 {
+			return nil
+		}
+		var data *byte
+		if err := arc.GetBuffer(uint32(frames), &data); err != nil {
+			return err
+		}
+		dst := unsafe.Slice(data, frames*frameBytes)
+		got := src.pull(frames * frameBytes)
+		n := copy(dst, got)
+		for i := n; i < len(dst); i++ {
+			dst[i] = 0 // silence-fill the shortfall
+		}
+		arc.ReleaseBuffer(uint32(frames), 0)
+		return nil
+	}
+
+	if err := feed(int(bufFrames)); err != nil { // pre-fill to avoid a start glitch
+		return err
+	}
+	if err := ac.Start(); err != nil {
+		return fmt.Errorf("start render: %w", err)
+	}
+	defer ac.Stop()
+
+	for {
+		select {
+		case <-stop:
+			return nil
+		default:
+		}
+		var padding uint32
+		ac.GetCurrentPadding(&padding)
+		if err := feed(int(bufFrames - padding)); err != nil {
+			return err
+		}
+		time.Sleep(8 * time.Millisecond)
+	}
+}