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

internal/audio/codec.go

@@ -0,0 +1,57 @@
+package audio
+
+import "fmt"
+
+// Codec converts between the wire payload of a network audio stream (Icom 50003)
+// and OpsLog's internal PCM (16 kHz mono 16-bit little-endian — the format the
+// capture/render engine and the pcmRing use). It exists so the transport code
+// (icomaudio.go) never hard-codes a format: today PCM is an identity passthrough;
+// tomorrow an Opus codec implements the same two methods and drops in unchanged.
+// This mirrors how civTransport abstracts the CAT byte stream from its transport.
+type Codec interface {
+	// Name is a short label for logs/UI.
+	Name() string
+	// Decode turns one received audio payload into internal PCM. The returned
+	// slice is freshly allocated (the caller may retain it).
+	Decode(payload []byte) ([]byte, error)
+	// Encode turns internal PCM into a payload to transmit.
+	Encode(pcm []byte) ([]byte, error)
+}
+
+// pcm16Codec is the uncompressed 16-bit-PCM codec — the Icom "uncompressed"
+// audio mode (rxcodec/txcodec in the conninfo). Icom sends little-endian 16-bit
+// mono samples, which is byte-for-byte OpsLog's internal format, so decode/encode
+// are copies. It is the Phase-4/5 default: zero-dependency, lossless, ideal on a
+// LAN. Opus (for WAN/internet bandwidth) becomes another Codec later.
+//
+// NOTE: rate conversion is deliberately NOT this layer's job. The Icom RX audio
+// is 16 kHz = our internal rate, so RX needs none. The rig's TX side may run at a
+// different rate (the captured conninfo showed 8 kHz) — Phase 5 will resample in
+// the TX path before Encode; keeping the codec rate-agnostic keeps that concern
+// in one place.
+type pcm16Codec struct{}
+
+// NewPCM16Codec returns the uncompressed 16-bit PCM codec.
+func NewPCM16Codec() Codec { return pcm16Codec{} }
+
+func (pcm16Codec) Name() string { return "pcm16" }
+
+func (pcm16Codec) Decode(payload []byte) ([]byte, error) {
+	// Icom PCM payloads are whole 16-bit samples; an odd length means a truncated
+	// packet — trim the stray byte rather than emit a half-sample click.
+	n := len(payload) &^ 1
+	if n != len(payload) {
+		if n == 0 {
+			return nil, fmt.Errorf("pcm16: payload too short (%d bytes)", len(payload))
+		}
+	}
+	out := make([]byte, n)
+	copy(out, payload[:n])
+	return out, nil
+}
+
+func (pcm16Codec) Encode(pcm []byte) ([]byte, error) {
+	out := make([]byte, len(pcm))
+	copy(out, pcm)
+	return out, nil
+}