Captioner.io

Captioner.io is a web-based tool that generates and edits subtitles for videos using AI. You upload a video file (MP4 or MOV), and it transcribes the speech to text with high accuracy, then lets you edit the timing and text directly in your browser. When you're done, you can export the subtitles as standard files (SRT, VTT, SBV) for use in other editing software, or download a new version of your video with the subtitles permanently added. It's designed specifically for video content rather than general transcription.

The tool uses OpenAI's Whisper model but has been optimized for video subtitles with extra processing for precise timestamp alignment and word-level controls. It supports over 98 languages and offers specific fine-tuning for dialects like Cantonese. A notable feature is the ability to import existing transcripts and have the tool automatically sync them to your video's audio, similar to YouTube's auto-sync but with claimed improvements. The editor comes in two versions: a simpler Express editor for quick jobs and a Pro editor with more control for detailed work.

This tool is most useful for video creators who regularly need accurate captions without spending hours on manual transcription and timing. YouTubers, social media marketers, and anyone producing educational or accessible video content will find it streamlines their workflow. The free tier allows testing with short videos, while paid plans remove watermarks, increase quality, and offer unlimited processing for longer projects.