audio-prep

Convert source audio into pretraining-ready WAV/FLAC, with validation and a dataset manifest as the handoff artifact to the pretraining pipeline. Discovery supports common FFmpeg-readable audio/video containers by default and can scan all files with --extensions all.

Defaults: 16 kHz, mono — the standard input spec for Wav2Vec2 / XLS-R style self-supervised speech pretraining. Override via CLI flags if a different downstream model needs something else.

Repo layout

audio-prep-pipeline/
├── src/audio_prep/
│   ├── config.py        # ConversionConfig: target spec + behavior knobs
│   ├── converter.py      # find_audio_files, convert_file, convert_batch
│   ├── validator.py      # probe_duration, validate_output
│   ├── chunker.py         # ChunkConfig, chunk_file, chunk_batch -- VAD speech chunking
│   ├── profiler.py        # Profiler, ProfileRecord -- runtime resource reports
│   ├── manifest.py       # build_manifest, write_manifest (JSONL output)
│   ├── exceptions.py     # ConversionError, ProbeError, ChunkingError
│   └── cli.py             # `audio-prep convert ...` / `audio-prep chunk ...` entry point
├── tests/
│   ├── conftest.py        # synthetic-audio fixtures (no binary files checked in)
│   ├── test_converter.py
│   ├── test_validator.py
│   ├── test_chunker.py    # fake-detector tests, no real VAD model needed
│   ├── test_manifest.py
│   └── test_cli.py
├── .github/workflows/ci.yml   # lint + typecheck + test matrix (3.10-3.12)
├── .pre-commit-config.yaml     # ruff + mypy + basic hygiene hooks, runs on every commit
├── pyproject.toml               # deps, ruff config, mypy config, pytest config
└── Makefile                      # `make check` runs everything CI runs, locally

Commands

audio-prep has two independent subcommands. Neither depends on the other running first -- both scan --input-dir for supported source files directly.

• audio-prep convert - conversion only: ffmpeg resample/remix/re-encode into the target WAV/FLAC spec, then validation, then an optional manifest. Does not chunk.
• audio-prep chunk - chunking only: VAD speech chunking straight from source audio, with Silero by default and Pyannote available for comparison. Does not convert or validate.

convert pipeline stages

1. discovery (find_audio_files) — recursively find supported source files under an input directory.
2. conversion (convert_file / convert_batch) — shell out to ffmpeg to resample/remix/re-encode into the target WAV/FLAC spec. Mirrors the input directory's subfolder structure on output. Runs in a process pool since each conversion is an independent subprocess call.
3. validation (validate_output) — re-opens each converted file with soundfile and checks it actually matches the requested sample rate, channel count, and minimum duration. This catches the case where ffmpeg exits 0 but silently produced something degenerate.
4. manifest (build_manifest / write_manifest) — JSONL file, one row per source file, recording status (ok / conversion_failed / validation_failed), output path, duration, sample rate, and any error.

Conversion failures don't abort the batch — a bad file in a 50,000-file corpus shows up as one conversion_failed row in the manifest, not a crashed job three hours in.

chunk pipeline stages

1. discovery (find_audio_files) — recursively find supported source files under an input directory.
2. chunking (chunk_file / chunk_batch) — runs the selected VAD backend over each file (decoding/resampling via ffmpeg) and splits it into speech-only chunks bounded by a [min, max] duration window, so silence-heavy source recordings don't waste pretraining compute.
3. manifest (build_chunk_manifest / write_manifest), optional — JSONL file, one row per source file, recording status (ok / chunking_failed), chunk count, and chunk paths.

Chunking failures (e.g. no speech detected) work the same way: chunk_batch returns a ChunkResult per file instead of raising.

Setup

# ffmpeg is a system dependency, not a pip package
sudo apt-get install ffmpeg   # or: brew install ffmpeg

pip install audio-prep-pipeline

Install directly from GitHub:

pip install "audio-prep-pipeline @ git+https://github.com/nattkorat/audio-prep-pipeline.git"

For local development:

make install   # pip install -e ".[dev]" + pre-commit install

The same install provides audio-prep convert, audio-prep chunk, Silero VAD, and Pyannote VAD support. FFmpeg/FFprobe are still system dependencies and must be available on PATH. Some Pyannote models require a Hugging Face token and accepted model terms. If the selected VAD backend cannot load in an offline environment, pass --allow-energy-fallback to use a lower-quality offline detector instead.

Usage

audio-prep convert

CLI:

audio-prep convert \
    --input-dir data/raw_mp3 \
    --output-dir data/wav16k \
    --format wav \
    --sample-rate 16000 \
    --workers 8 \
    --manifest data/manifest.jsonl \
    --profile profiles/convert.json

Python:

from pathlib import Path

from audio_prep import (
    ConversionConfig,
    build_manifest,
    convert_batch,
    validate_output,
    write_manifest,
)

config = ConversionConfig(
    output_format="wav",
    sample_rate=16_000,
    channels=1,
    num_workers=8,
)

results = convert_batch(Path("data/raw_mp3"), Path("data/wav16k"), config)
validations = {
    result.output: validate_output(result.output, config)
    for result in results
    if result.success and result.output is not None
}
records = build_manifest(results, validations)
write_manifest(records, Path("data/manifest.jsonl"))

audio-prep chunk

Independent of convert -- scans --input-dir for supported source files and runs VAD chunking directly against them, decoding (and resampling, if --sample-rate doesn't match the source) via ffmpeg:

CLI:

audio-prep chunk \
    --input-dir data/raw_mp3 \
    --output-dir data/chunks \
    --sample-rate 16000 \
    --format flac \
    --min-duration-sec 5 \
    --max-duration-sec 20 \
    --workers 4 \
    --manifest data/chunk_manifest.jsonl \
    --profile profiles/chunk-silero.json

Python:

from pathlib import Path

from audio_prep import ChunkConfig, build_chunk_manifest, chunk_batch, write_manifest

config = ChunkConfig(
    min_duration_sec=5,
    max_duration_sec=20,
    output_format="flac",
    sample_rate=16_000,
    num_workers=4,
    vad_backend="silero",
)

results = chunk_batch(Path("data/raw_mp3"), Path("data/chunks"), config)
records = build_chunk_manifest(results)
write_manifest(records, Path("data/chunk_manifest.jsonl"))

Compare VAD backends with the same input/settings:

audio-prep chunk \
    --input-dir data/raw_mp3 \
    --output-dir data/chunks-pyannote \
    --vad-backend pyannote \
    --pyannote-model pyannote/voice-activity-detection \
    --hf-token "$HF_TOKEN" \
    --profile profiles/chunk-pyannote.json

Python profiling:

from pathlib import Path

from audio_prep import ChunkConfig, Profiler, chunk_batch

profiler = Profiler()
config = ChunkConfig(vad_backend="pyannote", sample_rate=16_000, num_workers=1)

with profiler.measure("chunk", {"vad_backend": config.vad_backend}):
    results = chunk_batch(Path("data/raw_mp3"), Path("data/chunks-pyannote"), config)

profiler.write_json(
    Path("profiles/chunk-pyannote.json"),
    operation="chunk",
    metadata={"files": len(results), "vad_backend": config.vad_backend},
)

chunk_file itself doesn't care about source extension -- it decodes whatever path it's given -- so the Python API can also chunk an existing WAV/FLAC corpus (e.g. convert_batch output) by passing source_files explicitly instead of relying on chunk_batch discovery. This is an advanced Python API case:

from pathlib import Path

from audio_prep import ChunkConfig, ConversionConfig, build_manifest, chunk_batch
from audio_prep import convert_batch, validate_output

config = ConversionConfig(output_format="wav", sample_rate=16_000, channels=1, num_workers=8)
results = convert_batch(Path("data/raw_mp3"), Path("data/wav16k"), config)
validations = {
    result.output: validate_output(result.output, config)
    for result in results
    if result.success and result.output is not None
}
records = build_manifest(results, validations)

# source_files bypasses chunk_batch discovery, so this works
# directly against the already-converted WAV output above.
valid_outputs = [path for path, v in validations.items() if v.valid]
chunk_config = ChunkConfig(min_duration_sec=5, max_duration_sec=20, num_workers=4)
chunk_results = chunk_batch(
    Path("data/wav16k"),
    Path("data/wav16k/chunks"),
    chunk_config,
    source_files=valid_outputs,
)

Development workflow

make format     # ruff format + autofix
make lint       # ruff check
make typecheck  # mypy --strict
make test       # pytest with coverage
make check      # all of the above -- run this before opening a PR

pre-commit (installed via make install) runs ruff + mypy + basic hygiene checks automatically on every commit. CI (.github/workflows/ci.yml) re-runs the same checks plus the full test matrix across Python 3.10–3.12 on every push and PR.

Extending this

Natural next additions, in roughly the order they'd come up:

• Streaming manifest writes for very large corpora, instead of holding all ConversionResults in memory before writing.

Note: This is the template, that you have to extend from. Main branch is protected so you have to create another branch to work on.