How to Add Subtitles and Captions to Video

Subtitles vs Captions

Subtitles translate spoken dialogue for viewers who speak a different language. Captions transcribe all audio content — dialogue, sound effects, music descriptions — for viewers who cannot hear. Closed captions can be toggled on/off; open captions (burned in) are permanently visible.

Caption File Formats

SRT (SubRip Text) is the most widely supported format — simple timestamp and text pairs. WebVTT adds styling, positioning, and cue settings, making it ideal for web video. ASS/SSA supports complex formatting and animation, common in anime fansubs. TTML (Timed Text Markup Language) is the broadcast standard used by Netflix and other streaming services.

Creating Accurate Captions

Timing is critical — captions should appear when the speaker begins talking and disappear shortly after they stop. A maximum of two lines with 42 characters per line is the standard. Keep each caption on screen for at least 1 second and no more than 7 seconds. Avoid splitting sentences in the middle of a phrase.

Embedding Methods

Soft subtitles are separate tracks embedded in the video container (MKV, MP4) that viewers can toggle. Hard subtitles are burned into the video frames permanently. For web delivery, serve caption files separately and reference them in the video player using the HTML element.

Accessibility Standards

WCAG 2.1 Level A requires captions for all pre-recorded video with audio. Level AA requires captions for live video. The FCC mandates closed captions for television content distributed online. YouTube auto-generates captions but accuracy varies — always review and correct auto-generated captions.