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_enc_bits.go

@@ -0,0 +1,50 @@
+package amrnb
+
+// Encoder-side bit serialization, ported from opencore-amrnb prm2bits.cpp
+// (Int2bin/Prm2bits) and the ETS->IETF reordering in ets_to_wmf.cpp
+// (ets_to_ietf). The chain is: parameter array -> ETS serial bits (each
+// parameter expanded MSB-first to its bitno width) -> IETF storage bytes (the
+// ETS bits permuted by reorderBits and packed MSB-first). The leading ToC byte
+// is added by the payload layer, not here.
+
+// int2bin writes the low nBits of value into bits[0:nBits], MSB first
+// (bits[0] is the most significant bit). Mirrors Int2bin.
+func int2bin(value int16, nBits int, bits []int16) {
+	for i := nBits - 1; i >= 0; i-- {
+		bits[i] = value & 1
+		value >>= 1
+	}
+}
+
+// prm2bits expands the encoder parameter array prm into the ETS serial bit
+// array for the given speech mode (length modeBits[mode]). Mirrors Prm2bits.
+func prm2bits(mode Mode, prm []int16) []int16 {
+	bn := bitno[mode]
+	ets := make([]int16, modeBits[mode])
+	pos := 0
+	for i, w := range bn {
+		int2bin(prm[i], int(w), ets[pos:])
+		pos += int(w)
+	}
+	return ets
+}
+
+// etsToIetf permutes the ETS serial bits into IETF storage order via
+// reorderBits[mode] and packs them MSB-first into bytes. Mirrors the speech
+// branch of ets_to_ietf (without the ToC byte).
+func etsToIetf(mode Mode, ets []int16) []byte {
+	nb := modeBits[mode]
+	ro := reorderBits[mode]
+	out := make([]byte, (nb+7)/8)
+	for k := 0; k < nb; k++ {
+		bit := ets[ro[k]] & 1
+		out[k>>3] |= byte(bit) << uint(7-(k&7))
+	}
+	return out
+}
+
+// packFrame serializes a mode's encoder parameters into the RFC 4867 speech
+// payload bytes (IETF storage order), the inverse of mimeUnsort.
+func packFrame(prm []int16, mode Mode) []byte {
+	return etsToIetf(mode, prm2bits(mode, prm))
+}