glint_audio_pure 0.3.0

Pure-Dart MPEG-1 Layer III (MP3) encoder — no native code, no FFI, runs identically on every platform including the web. A pure-Dart sibling of the FFI-backed glint_audio, ported from the glint codec suite.

glint_audio_pure

A pure-Dart MP3 (MPEG-1 Layer III) encoder — no native code, no FFI, no runtime dependencies. It runs identically on every platform Dart targets, including the web, where FFI-backed codecs can't go.

It is the pure-Dart sibling of glint_audio (FFI bindings to the glint C++ codec suite). Use glint_audio when you want the full suite (MP3/AAC/Opus/WAV + resampling) at native speed; use glint_audio_pure when you need MP3 encoding that just works everywhere with zero setup.

import 'dart:typed_data';
import 'package:glint_audio_pure/glint_audio_pure.dart';

// pcm: mono samples in [-1, 1]
final Uint8List mp3 = mp3EncodeMono(pcm, sampleRate: 44100, bitrate: 128);
// -> a standard .mp3 any decoder plays.

Why

• All platforms, including web. Pure dart:core / dart:math / dart:typed_data. No dart:ffi, no bundled binaries, no build hooks.
• Standard output. Produces conformant MPEG-1 Layer III that ffmpeg, browser <audio>, and every other decoder play.
• Faithful port. Clean-room port of glint's encoder. The DSP front-end is machine-equivalent to the C++ reference (subband 5e-15, MDCT 7e-16 relative error) and the quantizer reproduces glint's per-granule decisions.

What it does

The full MPEG-1 Layer III encode pipeline:

1. 32-band polyphase (subband) analysis
2. MDCT — long blocks, with alias reduction and frequency inversion
3. Rate/distortion quantization loop with a psychoacoustic masking model: scalefactors are amplified to push quantization noise under the Bark-band masking threshold (Schroeder spreading + ATH), with scalefac_scale and preflag
4. Huffman coding (the ISO tables + count1 quads)
5. Constant-bitrate frame assembly (header + side info + main data)

Scope & quality

• Now: mono, constant bitrate, long blocks.
• Benchmarked against glint's own measure_audio.py on a speech signal at 128 kbps mono: SNR 35.2 dB (glint 32.1 dB), band 0–1 kHz 40.6 dB (glint 36.3). Raw SNR exceeds the reference; perceptual noise-to-mask (NMR) is a touch behind (a Huffman region-optimizer refinement — the next quality step). A 200→3000 Hz sweep decodes at 78 dB.
• Not yet: stereo, VBR, short/transient blocks, decode, AAC/Opus. Follow the repo for progress.

API

• Uint8List mp3EncodeMono(Float64List pcm, {int sampleRate = 44100, int bitrate = 128}) — encode mono PCM in [-1, 1] to a CBR .mp3. sampleRate ∈ {44100, 48000, 32000}; bitrate is any MPEG-1 rate (32…320 kbps).
• WAV helpers: readWavPcm16(bytes) → WavData, wavToMonoFloat(WavData) → Float64List.
• Frame constants: kMp3Bitrates, kMp3SampleRates, mp3FrameSize(...).

License

MIT. Ported from glint (MIT).