makesub

makesub is a command-line tool that automatically generates SRT subtitle files from any video or audio file. It uses OpenAI Whisper, a state-of-the-art speech recognition model, to transcribe spoken audio into accurate, timestamped subtitles.

No API key required. Everything runs locally on your machine.

makesub lecture.mp4
# → lecture.srt

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Who is this for?

• Content creators who want subtitles for YouTube videos, reels, or podcasts
• Developers building subtitle pipelines
• Researchers transcribing interviews or recordings
• Anyone who needs fast, offline, accurate subtitles from a video file

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Features

• Generates standard .srt subtitle files ready for use in any video editor or player
• Powered by OpenAI Whisper — no internet connection or API key needed after install
• Supports 99+ languages with automatic language detection
• Native Apple Silicon support (MPS acceleration on M1/M2/M3 Macs)
• Handles MP4, MOV, MKV, AVI, MP3, WAV, M4A, and any format ffmpeg can read
• Clear error messages for common problems (missing ffmpeg, no audio track, silent video, etc.)

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Requirements

• Python 3.9+
• ffmpeg — required for audio decoding

Install ffmpeg on macOS:

brew install ffmpeg

Install ffmpeg on Ubuntu/Debian:

sudo apt install ffmpeg

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Installation

pip install makesub

Apple Silicon (M1/M2/M3): Install PyTorch first to ensure you get the MPS-accelerated build, then install makesub:

pip install torch
pip install makesub

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Usage

makesub <video_or_audio_file> [options]

The subtitle file is written to the same directory as the input file by default.

makesub video.mp4
# Output: video.srt

Options

Flag	Default	Description
--model	auto	Whisper model: tiny, base, small, medium, large, large-v3, turbo, or auto to pick based on available memory
--language	en	Language code (e.g. en, fr, de, ja, zh). Use auto to detect automatically
--output	alongside input	Output .srt path or directory
--device	auto	Force compute device: cpu, mps, cuda
--verbose	off	Print each decoded segment in real time

Examples

# Subtitle an English video (default)
makesub interview.mp4

# Use a more accurate model for better results
makesub documentary.mp4 --model medium

# Auto-detect the spoken language
makesub foreign_film.mp4 --language auto

# Subtitle a French video
makesub podcast.mp3 --language fr

# Save the subtitle file to a specific location
makesub recording.mov --output ~/Desktop/recording.srt

# Watch segments appear in real time (useful for long files)
makesub lecture.mp4 --verbose

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Choosing a model

Larger models are slower but produce significantly more accurate subtitles. By default, makesub detects your available RAM and GPU memory and picks the largest model that fits comfortably.

Available memory	Auto-selected model
< 4 GB RAM	tiny
4–8 GB RAM	base
8–16 GB RAM	small
16 GB+ RAM	medium
2–5 GB VRAM	small / medium
10 GB+ VRAM	large-v3

You can always override with --model <name>.

Model	Size	Relative Speed	Best For
tiny	75 MB	~32x	Quick drafts, short clips
base	145 MB	~16x	Everyday use (default)
small	465 MB	~6x	Better accuracy, still fast
medium	1.5 GB	~2x	High accuracy
large-v3	3 GB	1x	Best possible accuracy
turbo	810 MB	~8x	Fast with good accuracy

Models are downloaded automatically on first use and cached in ~/.cache/whisper/.

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Supported file formats

Any format that ffmpeg can decode, including:

mp4 mov mkv avi webm flv m4v mp3 wav m4a aac ogg flac wma

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Troubleshooting

ffmpeg not found Install ffmpeg — see Requirements above.

No speech detected Try --language auto if the video is not in English. Check that the video actually has an audio track.

Not enough memory to load the model Switch to a smaller model: --model small or --model tiny.

Permission denied reading a file on macOS Terminal may need Full Disk Access. Go to System Settings > Privacy & Security > Full Disk Access and enable your terminal app.

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License

MIT

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Acknowledgements

Built on top of OpenAI Whisper. Audio decoding powered by ffmpeg.