feat(capability): 转码能力包（vendor 纯 Go AMR-NB 解码器 + 黄金向量逐样本对照 + 8 哨兵 + 注册面）

internal/capability/transcode/amrnb/dsp.go

@@ -0,0 +1,83 @@
+package amrnb
+
+// This file holds the AMR-NB signal-processing state and the entry points the
+// public Encoder/Decoder call per 20 ms frame. The fixed-point DSP itself
+// (LP analysis/LSF quantization, open/closed-loop pitch, algebraic codebook
+// search, gain quantization, synthesis and post-filtering, DTX) is a large
+// bit-exact port of 3GPP TS 26.090 — see opencore-amrnb (Apache-2.0), which
+// ships both encoder and decoder.
+//
+// The structs below define where that ported state lives. The encodeFrame /
+// decodeFrame methods are the single integration seam where the per-block DSP
+// functions are orchestrated per 20 ms frame.
+//
+// NOTE: the DSP is currently STUBBED — coder()/decoder() are not yet ported, so
+// encodeFrame emits a zero-filled bitstream of the correct size and decodeFrame
+// emits silence. The public API, RFC 4867 framing, fixed-point operators and
+// SIMD kernels are complete and exercised by the pure-Go tests; the bit-exact
+// DSP lands in a later phase (see the plan).
+
+// encoderState holds the persistent encoder analysis state across frames.
+type encoderState struct {
+	started bool
+	st      coderState
+}
+
+func (s *encoderState) reset() {
+	s.started = true
+	s.st.reset()
+}
+
+// encodeFrame analyses one 160-sample frame in the given mode and returns the
+// RFC 4867 frame payload bytes (the sorted/packed speech bits, without the
+// CMR/ToC header which the caller adds). Mirrors Speech_Encode_Frame: mask the 3
+// LSBs (13-bit input), high-pass + downscale (Pre_Process), run the analysis
+// (cod_amr), then serialize (prm2bits + IETF reorder via packFrame).
+func (s *encoderState) encodeFrame(mode Mode, samples []int16) ([]byte, error) {
+	if !s.started {
+		s.reset()
+	}
+	in := make([]int16, cL_FRAME)
+	for i := 0; i < cL_FRAME && i < len(samples); i++ {
+		in[i] = samples[i] &^ 7 // delete 3 LSBs (13-bit input)
+	}
+	s.st.pre.process(in, cL_FRAME)
+
+	prm, err := s.st.codAmr(int(mode), in)
+	if err != nil {
+		return nil, err
+	}
+	return packFrame(prm, mode), nil
+}
+
+// decoderState holds the persistent decoder synthesis state across frames.
+type decoderState struct {
+	dsp      decoderStateDSP
+	lastMode Mode
+	started  bool
+}
+
+func (s *decoderState) reset() {
+	s.dsp.reset()
+	s.lastMode = Mode1220
+	s.started = true
+}
+
+// decodeFrame decodes one parsed AMR-NB frame into 160 PCM samples. Good speech
+// frames are fully decoded; bad/SID/no-data frames currently emit silence
+// (error concealment and CNG are not yet ported).
+func (s *decoderState) decodeFrame(f frame) ([]int16, error) {
+	if !s.started {
+		s.reset()
+	}
+	synth := make([]int16, cAMR_NB_PCM_FRAME)
+	if f.ft <= FTMode1220 { // speech
+		mode := Mode(f.ft)
+		s.lastMode = mode
+		if f.q {
+			params := mimeUnsort(f.data, mode)
+			s.dsp.decodeSpeechFrame(int(mode), params, synth)
+		}
+	}
+	return synth, nil
+}