Subtitle Element

1. Shape

type SubtitleSource =
  | SubtitleWord[]
  | { $ref: string }
  | { src: string };

interface SubtitleClip extends BaseClip {
  type: "subtitle";
  words: SubtitleSource;
  config?: SubtitleConfig;
}

Also supports:

opacity
animations
keyframes
transition
transform
zIndex

2. `SubtitleWord`

interface SubtitleWord {
  word: string;
  punctuated_word: string;
  start: number;
  end: number;
  confidence?: number;
}

3. Supported subtitle sources

Inline array

{
  "words": [
    {
      "word": "hello",
      "punctuated_word": "Hello",
      "start": 0,
      "end": 0.4
    }
  ]
}

Subtitle asset via `$ref`

{
  "words": { "$ref": "subtitle-main" }
}

External URL

{
  "words": { "src": "https://example.com/subtitle.json" }
}

4. External subtitle URL rules

The remote endpoint must return JSON in one of these shapes:

SubtitleWord[]
{ "words": SubtitleWord[] }

Public behavior:

The preview flow accepts words: { "src": "..." }
Preview playback normalizes subtitle data before playback
If you send { src } directly into a lower-level renderer, subtitle data is not fetched automatically

5. `SubtitleConfig`

interface SubtitleConfig {
  mode?: "batch" | "stream";
  wordsPerBatch?: number;
  fontSize?: number;
  fontFamily?: string;
  fontWeight?: number | string;
  textAlign?: "left" | "center" | "right";
  textBoxWidth?: number | string;
  textColor?: string;
  highlightColor?: string;
  backgroundColor?: string;
  shadowColor?: string;
  shadowBlur?: number;
  borderColor?: string;
  borderWidth?: number;
  fadeInAnimation?: boolean;
  position?: "bottom" | "top" | "center";
  paddingBottom?: number;
}

6. Currently implemented config fields

mode
wordsPerBatch
fontSize
fontFamily
fontWeight
textAlign
textBoxWidth
textColor
highlightColor
backgroundColor
shadowColor
shadowBlur
borderColor
borderWidth
fadeInAnimation
position
paddingBottom

7. Mode behavior

`batch`

Displays subtitles in chunks
Highlights the currently spoken word

`stream`

Reveals words one by one

8. Whole-block animation behavior

Container-level subtitle animation applies to the full subtitle block, not to the per-word highlight logic.

Important distinction:

config.fadeInAnimation controls fade behavior inside subtitle batches
animations / keyframes / transition control the whole subtitle container

That means you can animate the subtitle block itself with fade, slide, or movement without changing the internal word-highlighting logic.

9. Example

{
  "type": "subtitle",
  "start": 0,
  "duration": 8,
  "words": { "$ref": "sub-main" },
  "animations": [
    { "type": "slideIn", "duration": 0.4, "direction": "up" }
  ],
  "config": {
    "position": "bottom",
    "fontSize": 60,
    "highlightColor": "#22d3ee",
    "backgroundColor": "rgba(0,0,0,0.4)"
  }
}

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