Video Subtitles
FFmpegAdd SRT subtitles to video with custom styling
Drag & drop files here, or click to select
Supports MP4, WebM, AVI, MOV, MKV and other common formatsFrequently Asked Questions
How It Works
The Subtitle tool uses FFmpeg WebAssembly with the subtitles filter (or ass filter) to burn SRT subtitles directly into video frames. This process is called hardcoding or hardsubbing — the text becomes part of the video's pixel data rather than a separate track.
The SRT (SubRip Subtitle) format is first parsed into a structured data model: each subtitle entry contains an index, start timestamp, end timestamp, and text content. The parser converts SRT timestamps (HH:MM:SS,mmm) to FFmpeg time format (HH:MM:SS.mmm).
FFmpeg renders each subtitle using FreeType font rendering with configurable parameters: font size (via force_style), font color, outline color, outline thickness, and vertical position. The subtitles filter applies these styles as ASS (Advanced SubStation Alpha) override tags. Each video frame is decoded, subtitles for the current timestamp are rendered as text overlays, and the composited frame is re-encoded.
Tips & Best Practices
- SRT format is simple: Index → Timestamp (start → end) → Text → Blank line. Keep this structure exact for reliable parsing.
- White text with black outline ensures readability on any background — the default style is purpose-built for maximum legibility.
- Font size scaling: Use larger fonts (20px+) for vertical 9:16 video and smaller fonts (16px) for horizontal 16:9.
- Position matters: Default bottom-center works for most content. Move subtitles higher for videos with important bottom-third graphics.
- Check timing first: Subtitle timing issues are the most common problem — verify timestamps align with speech before burning in.
- Keep lines short: Limit subtitle lines to 42 characters for optimal readability on mobile devices.
Use Cases
Content creators adding hardcoded subtitles to social media videos where platform auto-captions are unreliable or inaccurate.
Educational platforms embedding multilingual subtitles into course videos for accessibility and international audiences. Marketing teams adding captions to promotional videos for viewers who watch without sound on mobile. Film distributors hardcoding translated subtitles into foreign-language films for theatrical release. Accessibility advocates adding subtitles to all video content to make it accessible to hearing-impaired audiences. Social media managers creating subtitled versions of interview clips for platforms where audio doesn't auto-play.