LAC v1.4.0 - Compression & Performance Upgrade

Highlights

• Parallel block encoder/decoder
• Improved LPC
• Adaptive Rice k (v2)
• Smarter block-size heuristic
• Thread monitoring (--debug-threads now logs real worker thread IDs for both encode & decode)
• New LPC tests (-DLAC_BUILD_TESTS=ON test suite)

Performance

• Faster encode: up to 1.4-2.0x speed depending on sample rate and CPU cores
• Faster decode
• Lower file size: improved compression across all sample rates (44.1/48/96/192 kHz)
  (LAC still intentionally preserves bitstream compatibility.)

LAC v1.3.0 - Apple Silicon NEON Acceleration & Multithreaded Encoding

Highlights

• NEON SIMD acceleration for Apple Silicon
• Multithreaded block encoding
• New --debug-threads flag

Internal Improvements

• SIMD fallbacks fully synchronized with scalar logic
• Cleaned encode pipeline
• Precomputed Rice k-adaptation (SIMD-accelerated)
• No format changes - backward compatible

this entire optimization pass was completed in less than 24 hours lol

LAC v1.2.0 - Hi-Res (24-bit / 48-192 kHz) Support

New Features

• Added full support for 24-bit PCM at 44.1 / 48 / 96 / 192 kHz
• Bit-perfect lossless reconstruction verified
• Supports both L/R and Mid/Side stereo coding at all sample rates
• Expanded adaptive block size candidates up to 16384 samples for high-rate audio

Fixes

• Corrected internal handling of 24-bit PCM samples
• Removed unintended << 8 scaling that inflated residual magnitudes
• Restored proper Rice parameter adaptation for 24-bit signals
• Result: 24-bit .lac files now compress correctly (smaller than WAV)

Decoder / BitStream Hardening (Security & Stability)

Added strict bounds checks for:

• block_count (1 ... 10M)
• block_size (1 ... 16384)
• LPC order (1 ... 32 and < block_size)

BitReader now detects underflow and exposes error state

Validation

All formats successfully passed bit-perfect tests:

• 16-bit 44.1 kHz
• 24-bit 44.1 / 48 / 96 / 192 kHz

Both L/R and Mid/Side stereo paths confirmed identical to original WAV.

LAC v1.1.0 - Mid/Side Stereo Support

This release introduces optional Mid/Side (MS) stereo encoding for improved compression efficiency on stereo material, while keeping full compatibility with the LAC v1.0.0 bitstream format.

MS mode performs a reversible LR → M/S transform and often yields smaller file sizes on real music (typically 1–4% gains), especially when the left/right channels share similar content.

Mid/Side Stereo Encoding (optional)

• Added --stereo-mode=ms flag to lac_cli encode
• Default remains LR (standard Left/Right stereo)
• Provides bit-perfect LR reconstruction
• Verified with Python bit-perfect tests across full WAV files

Improvements

• Added decode-time benchmarks for LR vs MS in selftest
• Cleaner channel reconstruction path
• Additional internal validation for safe block parsing

CLI Usage
Encode (Mid/Side):
lac_cli encode input.wav output.lac --stereo-mode=ms

Decode:
lac_cli decode input.lac output.wav

LAC v1.0.0 - Lossless Audio Codec

This is the first stable release of LAC (Lossless Audio Codec), a lightweight, block-based lossless audio format designed for simplicity, speed, and transparency.

Key Features

• True lossless compression
  Verified bit-perfect reconstruction on large real-world stereo WAV files.
• LPC + Adaptive Rice entropy coding
  Efficient compression using 8-tap Q15 LPC and per-sample adaptive Rice parameter.
• Stereo support
  Independent L/R channel compression.
• Stable bitstream format
  Finalized structure for the LAC 1.0.0 stream.
• WAV I/O
  Supports PCM 16-bit / 44.1 kHz mono or stereo.
• CLI Tool (lac_cli)
  Encode: lac_cli encode input.wav output.lac
  Decode: lac_cli decode input.lac output.wav

Compression Performance

• Original WAV: 45.5MB
• LAC output: 32.4MB (29% reduction)

Bit-perfect verification
Roundtrip reconstruction matches the input exactly.