v1.2.0

Pure Go implementation of the Opus audio codec (RFC 6716 / RFC 8251). This is a
backward-compatible additive release over v1.1.1.

Public API expansion

• Multistream encoder/decoder APIs.
• Surround with standard channel mappings.
• Projection / Ambisonics (mapping families 2 and 3).
• Ogg Opus container (single logical stream).
• Packet extensions (RFC 8251 padding/extension parsing and generation).
• Repacketizer and packet padding helpers; packet-inspection helpers.
• 24-bit PCM (Encode24/Decode24) and float32 encode/decode.
• CELT phase-inversion controls; production codec controls, getters, and a
  libopus-defaults profile; automatic/maximum bitrate; broadened voice-mode rate
  policy.

In-band FEC (LBRR)

• SILK-only and hybrid in-band FEC encode and decode for mono and stereo
  (SetInbandFEC + non-zero packet-loss percentage). DecodeFEC reconstructs
  lost frames from the redundant copy; missing/inactive slots fall back to PLC.

SILK encoder quality

• Proper silk_find_LPC_FLP-path NLSF target (Burg LPC + A2NLSF), active NLSF
  interpolation, and voiced/unvoiced delayed-decision (trellis) NSQ.
• Fixed a low-F0 first-frame pitch misdetection (16 kHz speech-harmonic peak
  overshoot). On the AB scoreboard the encoder now matches or beats libopus on
  all 15 sampled cells (8/12/16 kHz × silence/unvoiced/steady/harmonic/onset).

Decoder

• RFC 8251 official vector suite at 12/12 PASS; verified against libopus 1.6.1
  via the opusref reference tests.

Hardening

• Expanded opusref interoperability CI, parser fuzz targets, PLC/FEC separation,
  and assorted defensive fixes (PLC pitch-history update at 16 kHz, packet
  padding overflow guard, content-hint reapply on encoder Reset).

Full changelog: v1.1.1...v1.2.0