Burn captions into a video

Burn subtitles into a video from an SRT, VTT, or ASS file, or auto-transcribe in any language, with full styling control.

The caption.burn job burns subtitles permanently into a video. Provide an SRT, VTT, or ASS file as the subtitles input, or omit it to auto-transcribe the audio. Style the text with web-hex colors, an outline, a background box, and a position.

Accepts: video · Type: caption.burn

Request

SDK

import { createClient, outputUrl } from "@rendobar/sdk";

const client = createClient({ apiKey: "rb_YOUR_KEY" });

const job = await client.jobs.create({
  type: "caption.burn",
  inputs: {
    source: "https://cdn.rendobar.com/assets/examples/sample.mp4",
    subtitles: "https://cdn.rendobar.com/assets/examples/sample.srt",
  },
  params: { fontFamily: "Inter", fontSize: 48, boxEnabled: true },
});

const result = await client.jobs.wait(job.id);
console.log(outputUrl(result));

Omit subtitles to auto-transcribe. The spoken language is detected by default (language: "auto"). Pass an ISO-639-1 code to skip detection.

Inputs

source · string · required

URL of the source video to caption.

subtitles · string

URL of an SRT, VTT, or ASS subtitle file. A provided ASS file is burned as-is, preserving its own styling. Omit to auto-transcribe the audio.

Parameters

language · enum · default: "auto"

Spoken language for the auto-transcribe path, as an ISO-639-1 code (e.g. en, es, ja) or auto to detect. English uses a faster model. Everything else routes to multilingual transcription. Ignored when a subtitle file is provided.

fontFamily · string · default: "Inter"

Font family. Must resolve to a font available to the renderer.

fontSize · integer · default: "48"

Font size in output pixels. Range 8–400.

fontColor · string · default: "#FFFFFF"

Text fill color as web hex (#RRGGBB or #AARRGGBB, alpha first).

bold · boolean · default: "true"

Render the text bold.

italic · boolean · default: "false"

Render the text italic.

outlineColor · string · default: "#000000"

Outline (stroke) color as web hex.

outlineWidth · number · default: "2"

Outline thickness in pixels. Range 0–20.

shadow · number · default: "1"

Drop-shadow depth in pixels. Range 0–20. 0 disables the shadow.

boxEnabled · boolean · default: "false"

Draw a filled background box behind the text (the accessibility “subtitle bar”).

boxColor · string · default: "#000000"

Background box color as web hex. Applies when boxEnabled is true.

boxOpacity · number · default: "0.6"

Background box opacity, 0 (transparent) to 1 (opaque).

position · enum · default: "bottom"

Vertical placement. One of bottom, center, top.

alignment · enum · default: "center"

Horizontal alignment. One of left, center, right.

marginV · integer · default: "60"

Vertical margin in pixels. Range 0–2000.

marginH · integer · default: "40"

Horizontal margin in pixels. Range 0–2000. Also bounds the line-wrap width.

maxCharsPerLine · integer

Maximum characters per line on the auto-transcribe path. Range 10–80.

Like every job, this returns the standard response. See Job output for the shape and how to read the result.

For animated word-level captions instead, see captions.animate.