subtool 0.0.2

Local subtitle generation and translation CLI using Whisper and NLLB-200

lsub

Local AI-powered subtitle generation and translation

Extract and translate video subtitles using Whisper and NLLB-200.

Features

• Automatic speech recognition using OpenAI Whisper (auto-detects language)
• Multi-language translation using Meta's NLLB-200 model
• Subtitle embedding into video files (MP4 or MKV)
• Multiple subtitle tracks with proper language naming
• SRT and ASS format support (ASS for better Unicode/CJK character rendering)

Install

Recommended (fast, reproducible):

uv tool install lsub

Run without installing:

uvx lsub video.mp4 -t en es

With pip:

pip install lsub

Usage

# Basic usage - extract subtitles (auto-detect language)
lsub video.mp4

# Extract and translate to English and Spanish
lsub video.mp4 -t en es

# Specify source language explicitly
lsub video.mp4 -l zh -t en

# Use different Whisper model (default: turbo)
lsub video.mp4 -m large -t en

# Output as MKV (better subtitle support for Unicode/CJK)
lsub video.mp4 -t en zh -f mkv

# Generate SRT files only (no embedding)
lsub video.mp4 -t en es --srt-only

# Custom output path
lsub video.mp4 -t en -o output_with_subs.mp4

Supported Languages

Translation supports 12 common languages:

• en - English
• es - Spanish
• fr - French
• de - German
• it - Italian
• pt - Portuguese
• ru - Russian
• ja - Japanese
• ko - Korean
• zh - Chinese
• ar - Arabic
• hi - Hindi

More languages available in NLLB-200 documentation.

Whisper Models

Available models (trade-off between speed and accuracy):

• tiny - Fastest, least accurate
• base - Fast, decent accuracy
• small - Balanced
• medium - Good accuracy, slower
• large - Best accuracy, slowest
• turbo - Fast and accurate (default)

Output Formats

• MP4 (default): Compatible but limited Unicode support for subtitles
• MKV: Better subtitle support, recommended for Chinese/Japanese/Korean content

MKV uses ASS format with embedded font information for proper CJK character rendering.

Development

uv sync
uv run lsub video.mp4 -t en     # run the CLI using local code

# optional: editable install
uv pip install -e .

./scripts/release.sh            # release a new version

Notes

• First run downloads Whisper model (~1.5GB for turbo) and NLLB-200 model (~1.2GB)
• Models are cached in ~/.cache/huggingface/
• Requires ffmpeg installed on your system
• Generated subtitle files (.srt and .ass) are saved alongside the video
• For best CJK (Chinese/Japanese/Korean) subtitle rendering, use MKV format (-f mkv)