mtt-transcriber 0.1.0

Transcribe, translate, dub, and caption audio/video from files or YouTube URLs.

Media Transcriber Suite

Transcribe, translate, caption, and dub video/audio — from a YouTube URL or from your own uploaded files — all in Streamlit.

What's in here

File	What it does
transcriber_app.py	Launcher. Sidebar lets you pick "YouTube URL" or "Upload a File", then dispatches to one of the two apps below. Run this one.
youtube_transcriber.py	Paste YouTube URL(s) (one or many, one per line) → embedded player(s) with synced/overlaid captions, translation, dubbed audio, and MP4 export with burned-in captions. Batch mode: one tab per video.
media_file_transcriber.py	Upload your own audio/video file(s) → same feature set, plus batch mode (multiple files, each in its own tab).
cli.py	Command-line interface — same engine as both apps above, no browser needed. Good for scripting/automation.
pyproject.toml	Packaging config — installs cli.py as a standalone mtt command (see below).
requirements.txt	Python dependencies.

Each app file is also fully runnable on its own (streamlit run youtube_transcriber.py), independent of the launcher.

Features

• Playback with synced captions: transcript segments highlight and auto-scroll in time with the video/audio, and can also be overlaid directly on the video (or shown as a big "lyrics" line for audio-only files).
• Transcription via faster-whisper (choose model size: tiny → large-v3).
• Translation to 14 languages (including English) via Google Translate (free, through deep-translator), with a choice of showing Original / Translated / Both. Source language is auto-detected, so this also covers translating non-English audio into English.
• Dubbed audio via edge-tts: synthesizes each translated line and times it to the original segment, speeding lines up (capped, to stay intelligible) when they'd otherwise run long and overlap the next one. This is an approximation of a real dub, not a polished one — see Limitations below.
• Export:
  • Downloadable .txt transcripts (original and/or translated).
  • Downloadable audio-only .mp3 (original track, or the dubbed track).
  • Downloadable .mp4 with captions burned in permanently (hardcoded via ffmpeg's subtitles filter). For audio-only uploads, this instead synthesizes a simple "lyric video" (solid background, optional waveform) so you still get a shareable video.
• Batch mode (file-upload app only): upload several files at once, each gets its own tab named after the file. A "Transcribe All" button queues transcription across all of them sequentially.
• Broad format support for uploads: audio .mp3 .wav .m4a .aac .flac .ogg .opus .wma, video .mp4 .m4v .webm .mov .mkv .avi .flv.
• Sensible filenames: downloads are named after the source (video title for YouTube, original filename for uploads), tagged with _orig / _dubbed_<lang> / _transcript_<lang> etc., so multiple downloads don't collide or get confusing.

CLI

cli.py is a thin wrapper around the exact same functions the two Streamlit apps use — it imports them directly, so there's no separate implementation to drift out of sync. Must live in the same folder as youtube_transcriber.py and media_file_transcriber.py.

# Transcribe two local files to plain text
python cli.py --input_type file --source clip1.mp3 clip2.mp4 --output_type txt

# Transcribe + translate a YouTube video to Japanese, get a captioned MP4 and a dubbed MP3
python cli.py --input_type url --source https://youtu.be/XXXXXXXXXXX \
    --output_type mp4 mp3 --target-lang Japanese

# Batch: several files, every output type, translated to English
python cli.py --input_type file --source a.mp3 b.mp4 c.wav \
    --output_type txt mp3 mp4 --target-lang English --model small

# See available target languages
python cli.py --list-languages

Required flags: --input_type {file,url}, --source (one or more paths/URLs), --output_type (one or more of txt mp3 mp4).

Useful optional flags: --model (Whisper size, default base), --target-lang (enables translation), --display-mode ("Original only" / "Translated only" / "Both" — controls what goes into .txt/.mp4 output when translating), --quality (YouTube MP4 export resolution), --resolution/--bg-color/--waveform (lyric-video export for audio file uploads), --output-dir (default ./output).

Behaves like the UI's batch mode: duplicate sources are detected and skipped (by video ID for URLs, by absolute path for files), YouTube downloads get a short pause between them, and a failed source is logged and skipped rather than aborting the whole run — exit code is 1 if anything failed, 0 otherwise.

Installing it as a standalone mtt command

pyproject.toml registers cli.py's main() as a console-script entry point, so an editable install gives you a real mtt command on your PATH — no more typing python cli.py, and no more needing to run it from inside the project folder:

pip install -e .
mtt --list-languages          # works from anywhere now
mtt --input_type file --source clip.mp3 --output_type txt

This is also the scaffold for turning this into a proper published pip package later — pyproject.toml already declares the dependencies and the mtt entry point; publishing would mainly mean choosing a real package name/version and running through build/twine (or similar), rather than restructuring anything here.

Setup

1. Python dependencies

pip install -r requirements.txt

2. ffmpeg (system dependency — not a pip package)

You need ffmpeg on your PATH, built with libass support (needed for the subtitles filter that burns in captions). Check with:

ffmpeg -filters | grep subtitles      # macOS/Linux
ffmpeg -filters | findstr subtitles   # Windows

You should see lines for both ass and subtitles filters. If not, your ffmpeg build is missing libass — this is common with minimal builds (e.g. some conda-forge installs). Get a full build instead:

• macOS: brew install ffmpeg (Homebrew's build includes libass)
• Ubuntu/Debian: sudo apt-get install ffmpeg (or build from a static source if your distro's package is minimal)
• Windows: grab a static build from the community builders linked on ffmpeg.org's download page — e.g. BtbN/FFmpeg-Builds (win64-gpl build), extract it, and add its bin folder to your PATH.

If you have multiple ffmpeg installs (e.g. conda-forge and a full build), Windows/macOS/Linux all just use whichever comes first in PATH — run ffmpeg -version in a fresh terminal to confirm which one is active.

Running it

streamlit run transcriber_app.py

This opens the launcher with a sidebar toggle between the YouTube and file-upload flows. Or run either app directly if you only need one:

streamlit run youtube_transcriber.py
streamlit run media_file_transcriber.py

Usage notes

• Transcribe first, then optionally enable translation in the sidebar — translation re-runs automatically when you change the target language or display mode, but transcription itself only re-runs when you click the button (and only if the model size changed).
• Batch mode: both apps support processing multiple items at once — paste several YouTube URLs (one per line) or upload multiple files — each gets its own tab named after its source. "Transcribe All" queues transcription across all of them sequentially (Streamlit is single-threaded per session, so this isn't parallel), then open individual tabs to translate/export each one. Duplicate items (same video ID, or identical file content) are detected and skipped with a warning rather than erroring. Video export (MP4 with burned-in captions) stays a deliberate per-tab action in both apps — it's the heaviest operation, so it's not batched.
• MP4 export re-encodes the video track (audio is stream-copied), so it's slower than transcription — expect it to take a while on longer/higher-resolution videos.
• Files embedded for the custom player/overlay in the upload app are inlined as base64, so very large uploads (100+ MB) will be slow to preview in-browser; transcription/translation/export aren't affected.
• YouTube batch mode is network-bound (each video is actually downloaded), so it's noticeably slower per item than file batch mode and scales with video count accordingly. There's a short delay between downloads to be gentler on YouTube, but a large batch can still take a while — and is more exposed to YouTube-side rate limiting than local files ever would be.

Limitations

• Translation uses the free, unofficial Google Translate backend (via deep-translator) — good for everyday use, not a professional MT service, and requires internet access.
• Source language is auto-detected, not user-specified — this works for any spoken language (transcription and translation aren't locked to English), but manually specifying it when you already know it (e.g. language="es") would improve both speed and accuracy. Not yet exposed as an option.
• Dubbed audio is an approximation: TTS pacing rarely matches the original speaker exactly. Lines are sped up by up to 50% to try to fit their original time slot; anything that would need more than that to fit will still overlap somewhat. Treat it as "get the gist in another language," not a lip-synced dub.
• edge-tts is an unofficial, reverse-engineered wrapper around Microsoft's Read Aloud service (same category of tool as the free Google Translate backend above) — free and keyless, but not an official/supported API.
• A few uploaded formats (.wma, .mov, .mkv, .avi, .flv) commonly don't play back natively in the browser's preview player even though transcription/translation/export all still work fine on them — the app flags this when it applies.
• st.cache_data/st.cache_resource are used throughout to avoid redoing expensive work (transcription, translation, rendering), keyed by content hash (uploads) or video ID (YouTube) plus the relevant settings — so switching a model size or target language will trigger fresh work the first time, then reuse it afterward.