Subtitle

Embed or burn subtitles into video. Supports both soft subtitles (selectable in the media player) and hard-burned subtitles (baked into the video stream).

Quick example

import { ffmpeg } from "ffmpeg-kit";

// Soft subtitles (selectable in player)
await ffmpeg.subtitle()
  .input("video.mp4")
  .softSub({ path: "subs.srt", language: "en" })
  .output("with-subs.mkv")
  .execute();

API

.input(path)

Input video file. Required.

.softSub(options)

Embed subtitle track as a selectable stream (MKV or MP4 container).

Parameter	Type	Default	Description
path	string	—	Path to subtitle file (.srt, .ass, .vtt)
language	string	"und"	ISO 639-1 language code ("en", "fr", etc.)
title	string	—	Track title shown in player
default	boolean	false	Set as default subtitle track
forced	boolean	false	Mark as forced (always shown)

Container support

Soft subtitles require MKV (.mkv) or MP4 (.mp4) output. MP4 supports only mov_text subtitle codec. Use MKV for ASS/SSA format preservation.

.hardBurn(options)

Burn subtitles permanently into the video stream.

Parameter	Type	Default	Description
path	string	—	Path to subtitle file
fontDir	string	—	Directory to search for fonts (for ASS)
charEncoding	string	"UTF-8"	Character encoding of the subtitle file

.output(path)

Output file path. Required.

Examples

Embed SRT as soft subtitles

await ffmpeg.subtitle()
  .input("video.mp4")
  .softSub({
    path: "english.srt",
    language: "en",
    title: "English",
    default: true,
  })
  .output("with-subs.mkv")
  .execute();

Hard-burned ASS subtitles

await ffmpeg.subtitle()
  .input("video.mp4")
  .hardBurn({
    path: "styled.ass",
    fontDir: "./fonts",
  })
  .output("burned.mp4")
  .execute();

Multiple subtitle tracks

await ffmpeg.subtitle()
  .input("video.mp4")
  .softSub({ path: "en.srt", language: "en", default: true })
  .softSub({ path: "fr.srt", language: "fr" })
  .softSub({ path: "de.srt", language: "de" })
  .output("multilang.mkv")
  .execute();

Result type

interface SubtitleResult {
  outputPath: string;
  duration: number;
  size: number;
  subtitleTracks: number;
  probeResult: ProbeResult;
}

Related

• Text — burn dynamic text overlays using drawtext
• Export — re-encode video while adding subtitles