BLOS Audio Codec

BLOS is a minimal, experimental, single-file audio format and codec written in C. It achieves compression ratios of 5–6% on 16-bit WAV files, while staying simple and hackable.

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Why BLOS?

Most modern audio codecs are big, complex, and dependency-heavy. BLOS takes the opposite route:

• A single C file you can read in one sitting.
• A format that’s easy to inspect, tinker with, and extend.
• Compression that’s not the tightest on Earth, but transparent and surprisingly efficient for its size.

It’s designed as a playground for learning about LPC, residual coding, and audio compression basics, while still being usable for actual audio storage.

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Features

• Single C file – no external dependencies beyond libsndfile and math. *LPC compression with Levinson-Durbin algorithm.
• Rice coding for residuals.
• Mid/Side stereo coding for efficient stereo compression.
• Transient bypass for large residuals (stores raw samples when necessary).
• Frame-based, bit-packed, aligned stream format.
• Compression ratios around 5–6% on typical audio material.

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Building

Make sure you have libsndfile installed.

On Linux:

sudo apt install libsndfile1-dev   # Debian/Ubuntu
# or
sudo pacman -S libsndfile          # Arch

Then clone and build:

git clone https://github.com/vbloom-x3/audio-format
cd audio-format
make

This will produce the executable:

./codec

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##Usage

Encode a WAV file

To compress a raw WAV file into .blos format:

./codec input.wav output.blos

Example:

Original waveform (input.wav):

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Decode a BLOS file

To decompress a .blos file back into a playable WAV:

./codec -d input.blos output.wav

Example:

Decoded waveform (output.wav):

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File Format Overview

• Magic: "BLOS"

• Header: sample rate, frame count, channel count, frame size.

• Frames:

  • Seeds (initial samples for prediction).
  • Float64 LPC coefficients.
  • Residuals encoded with Rice coding.
  • Escapes for transient bypass.

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Example Output

During encoding you’ll see progress and per-frame stats:

[Encode] frames=1234 frame_size=512
Frame 1/1234: order=12 kA=4 kB=5 meanA=8.2 meanB=7.5 escA=0 escB=2
Encoded frame 1/1234
...
[Encode] done: output.blos

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License

This project is licensed under the GNU General Public License v3.0. You may redistribute and/or modify it under the terms of the GPLv3.

For details, see the LICENSE file.

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Notes

• This is experimental—expect quirks and possible artifacts.
• Future improvements might include entropy coding, adaptive thresholds, and better stereo handling.

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