📖 Quick Start Guide & FAQ

How to Add Subtitles to Your Video

Captioner is a completely free offline tool to add captions to your videos. All speech recognition and subtitle rendering happen entirely inside your web browser. No files are uploaded to any external servers, ensuring complete privacy.

  1. Import Media: Click Upload to select any local video (MP4, WebM) or audio (MP3, WAV) file under 1 hour.
  2. Wait for AI Engine: On your first visit, the browser will download a lightweight AI voice recognition model (~150MB). Once downloaded, it is cached locally in your browser for instant future use.
  3. Generate Subtitles: Click the green Process button. The built-in AI will analyze the speech track and automatically partition and translate it into synchronized subtitles.

Edit, Align, and Export Your Subtitles

Once generated, you can refine your subtitles using the interactive timeline editor, make frame-by-frame adjustments, and export the finished video with hardcoded subtitles.

  1. Modify Subtitle Text: Double-click any caption card in the editor to modify the text in real-time.
  2. Adjust Timings: Tap the timestamp badges next to any caption to adjust the start and end times with millisecond precision, ensuring perfect sync.
  3. Burn & Download: Click the red Export button to render your subtitles directly onto the video frames. The app will generate and download the completed video file to your local computer.

Frequently Asked Questions (FAQ)

Q: Why does the first load take some time?
A: The first visit downloads the offline voice recognition model files. Future loads will launch instantly since the files are securely cached in your web browser storage.
Q: Are my personal videos or audio files secure?
A: Yes. All subtitle transcription, audio slicing, and video generation occur locally on your machine. Zero data is sent to the internet or any cloud server.
Q: Is there a video length limit?
A: Yes, files are limited to 1 hour to prevent your browser from running out of system memory and closing the tab.
Q: What do labels like <|Laughter|> mean in my subtitles?
A: The intelligent voice engine detects non-speech audio events (such as laughter, crying, applause, or coughing) and marks them so you can include emotion and context in your subtitles. You can edit or delete them as you wish.