Update Caption Presets - SvelteKit

Extend CE.SDK’s video caption feature with custom caption presets by updating the content.json file. Caption presets let your users apply predefined styles to video captions with a single click.

Update Caption Presets example showing a styled neon glow caption preset

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Video captions have become an essential part of digital content, improving accessibility and engagement. With CE.SDK’s caption presets feature, you can offer your users a selection of predefined caption styles that they can apply with a single click. This guide shows you how to create styled text blocks, serialize them as preset files, and structure the content.json to make them available in the caption presets panel.

import type { EditorPlugin, EditorPluginContext } from '@cesdk/cesdk-js';
import packageJson from './package.json';

/**
 * CE.SDK Plugin: Update Caption Presets Guide
 *
 * Demonstrates creating custom caption presets in CE.SDK:
 * - Creating a styled text block as a preset base
 * - Applying neon glow styling with colors and drop shadow
 * - Serializing the block for use as a preset file
 * - Understanding the content.json structure for caption presets
 */
class Example implements EditorPlugin {
  name = packageJson.name;

  version = packageJson.version;

  async initialize({ cesdk }: EditorPluginContext): Promise<void> {
    if (!cesdk) {
      throw new Error('CE.SDK instance is required for this plugin');
    }

    // Enable video editing features for caption presets
    cesdk.feature.enable('ly.img.video');
    cesdk.feature.enable('ly.img.timeline');
    cesdk.feature.enable('ly.img.playback');

    // Load assets and create a video scene
    await cesdk.addDefaultAssetSources();
    await cesdk.addDemoAssetSources({
      sceneMode: 'Video',
      withUploadAssetSources: true
    });
    await cesdk.createVideoScene();

    const engine = cesdk.engine;

    // Create a text block to use as the preset base
    // Text blocks support all the styling properties needed for captions
    const textBlock = engine.block.create('text');

    // Set sample caption text
    engine.block.setString(textBlock, 'text/text', 'NEON GLOW');

    // Position and size the text block
    engine.block.setPositionX(textBlock, 50);
    engine.block.setPositionY(textBlock, 200);
    engine.block.setWidth(textBlock, 600);
    engine.block.setHeightMode(textBlock, 'Auto');

    // Style the text with a bright neon cyan color
    // This will be the fill/solid/color property in the preset
    engine.block.setColor(textBlock, 'fill/solid/color', {
      r: 0.0,
      g: 1.0,
      b: 1.0,
      a: 1.0
    });

    // Set font properties for the caption style
    engine.block.setFloat(textBlock, 'text/fontSize', 48);

    // Use a bold font for better visibility
    // Load and set a typeface
    const typefaceResult = await engine.asset.findAssets('ly.img.typeface', {
      query: 'Roboto',
      page: 0,
      perPage: 10
    });

    if (typefaceResult.assets.length > 0) {
      const typefaceAsset = typefaceResult.assets[0];
      const typeface = typefaceAsset.payload?.typeface;
      if (typeface && typeface.fonts?.[0]?.uri) {
        engine.block.setFont(textBlock, typeface.fonts[0].uri, typeface);
      }
    }

    // Add a glowing drop shadow effect for the neon look
    // This creates the characteristic neon glow effect
    engine.block.setDropShadowEnabled(textBlock, true);

    // Set glow color (bright cyan to match text)
    engine.block.setColor(textBlock, 'dropShadow/color', {
      r: 0.0,
      g: 1.0,
      b: 1.0,
      a: 0.8
    });

    // Configure shadow properties for a soft glow
    engine.block.setFloat(textBlock, 'dropShadow/blurRadius/x', 20);
    engine.block.setFloat(textBlock, 'dropShadow/blurRadius/y', 20);
    engine.block.setFloat(textBlock, 'dropShadow/offset/x', 0);
    engine.block.setFloat(textBlock, 'dropShadow/offset/y', 0);

    // Optionally add a semi-transparent dark background
    // This helps the caption stand out against video content
    engine.block.setBackgroundColorEnabled(textBlock, true);
    engine.block.setColor(textBlock, 'backgroundColor/color', {
      r: 0.0,
      g: 0.0,
      b: 0.1,
      a: 0.7
    });

    // Add the styled text block to the page
    const pages = engine.block.findByType('page');
    if (pages.length > 0) {
      engine.block.appendChild(pages[0], textBlock);
    }

    // Select the block and zoom to it so it's visible in the editor
    engine.block.select(textBlock);
    await engine.scene.zoomToBlock(textBlock, { padding: 40 });

    // Serialize the styled text block to create a preset file
    // This serialized string can be saved as a .blocks or .preset file
    // Include 'bundle' scheme to allow serialization of blocks with bundled fonts
    const serializedPreset = await engine.block.saveToString(
      [textBlock],
      ['buffer', 'http', 'https', 'bundle']
    );

    console.log('=== Serialized Preset ===');
    console.log('Save this as a .preset file (e.g., neon-glow.preset):');
    console.log(serializedPreset);

    // Example content.json entry for the custom preset
    // This shows the structure needed to add the preset to content.json
    const contentJsonEntry = {
      id: '//ly.img.captionPresets/neon-glow',
      label: {
        en: 'Neon Glow'
      },
      meta: {
        uri: '{{base_url}}/ly.img.captionPresets/presets/neon-glow.preset',
        thumbUri: '{{base_url}}/ly.img.captionPresets/thumbnails/neon-glow.png',
        mimeType: 'application/ubq-blocks-string'
      },
      payload: {
        properties: [
          {
            type: 'Color',
            property: 'fill/solid/color',
            value: { r: 0.0, g: 1.0, b: 1.0, a: 1.0 },
            defaultValue: { r: 0.0, g: 1.0, b: 1.0, a: 1.0 }
          },
          {
            type: 'Color',
            property: 'dropShadow/color',
            value: { r: 0.0, g: 1.0, b: 1.0, a: 0.8 },
            defaultValue: { r: 0.0, g: 1.0, b: 1.0, a: 0.8 }
          },
          {
            type: 'Color',
            property: 'backgroundColor/color',
            value: { r: 0.0, g: 0.0, b: 0.1, a: 0.7 },
            defaultValue: { r: 0.0, g: 0.0, b: 0.1, a: 0.7 }
          }
        ]
      }
    };

    console.log('\n=== content.json Entry ===');
    console.log('Add this entry to your content.json assets array:');
    console.log(JSON.stringify(contentJsonEntry, null, 2));

    // Example of a complete content.json file structure
    const completeContentJson = {
      version: '3.0.0',
      id: 'ly.img.captionPresets',
      assets: [contentJsonEntry]
    };

    console.log('\n=== Complete content.json Example ===');
    console.log(JSON.stringify(completeContentJson, null, 2));

    console.log('\n=== Caption Preset Guide ===');
    console.log(
      'The styled text block above demonstrates a "Neon Glow" caption preset.'
    );
    console.log('To use this preset:');
    console.log('1. Save the serialized preset string as a .preset file');
    console.log('2. Create a thumbnail image showing the preset appearance');
    console.log('3. Add the content.json entry to your assets folder');
    console.log('4. Configure CE.SDK baseURL to point to your assets location');
  }
}

export default Example;

This guide covers how to understand the caption presets folder structure, create custom caption styles from text blocks, serialize presets for hosting, define customizable properties, and configure CE.SDK to load your custom presets.

Understanding the Caption Presets Structure#

Folder Organization#

CE.SDK’s caption presets use a specific directory structure that the engine expects when loading presets. The base path is assets/v4/ly.img.captionPresets/ and contains:

assets/v4/ly.img.captionPresets/
├── content.json                # Master index of all presets
├── presets/                    # Folder containing preset files
│   ├── my-custom-preset.preset # Serialized caption block with styling
│   └── ...
└── thumbnails/                 # Folder containing preview images
    ├── my-custom-preset.png    # Preview image for preset
    └── ...

The main content.json file acts as an index that lists all available presets with their metadata. When CE.SDK loads caption presets, it reads this file to discover available presets and their locations.

content.json Format#

The content.json file follows a specific format with version, asset source ID, and an assets array:

{
  "version": "3.0.0",
  "id": "ly.img.captionPresets",
  "assets": [
    {
      "id": "//ly.img.captionPresets/my-preset",
      "label": { "en": "My Preset" },
      "meta": {
        "uri": "{{base_url}}/ly.img.captionPresets/presets/my-preset.preset",
        "thumbUri": "{{base_url}}/ly.img.captionPresets/thumbnails/my-preset.png",
        "mimeType": "application/ubq-blocks-string"
      },
      "payload": {
        "properties": []
      }
    }
  ]
}

Each asset entry requires a unique ID with namespace, localized label, meta with URIs and mime type, and optional payload properties for customization.

Creating Custom Caption Presets#

Designing a Caption Style#

We create a styled text block as the basis for our preset. Text blocks support all the styling properties needed for captions including colors, fonts, backgrounds, shadows, and effects.

// Create a text block to use as the preset base
// Text blocks support all the styling properties needed for captions
const textBlock = engine.block.create('text');

// Set sample caption text
engine.block.setString(textBlock, 'text/text', 'NEON GLOW');

// Position and size the text block
engine.block.setPositionX(textBlock, 50);
engine.block.setPositionY(textBlock, 200);
engine.block.setWidth(textBlock, 600);
engine.block.setHeightMode(textBlock, 'Auto');

We position and size the text block, then set sample caption text. The text block serves as our canvas for applying the styling that will define the preset’s appearance.

Styling with Colors and Fonts#

We style the text with colors and configure font properties. The fill color becomes the fill/solid/color property in the preset:

// Style the text with a bright neon cyan color
// This will be the fill/solid/color property in the preset
engine.block.setColor(textBlock, 'fill/solid/color', {
  r: 0.0,
  g: 1.0,
  b: 1.0,
  a: 1.0
});

We also configure font size and load a typeface. When users apply this preset, their captions will inherit these font settings:

// Set font properties for the caption style
engine.block.setFloat(textBlock, 'text/fontSize', 48);

// Use a bold font for better visibility
// Load and set a typeface
const typefaceResult = await engine.asset.findAssets('ly.img.typeface', {
  query: 'Roboto',
  page: 0,
  perPage: 10
});

if (typefaceResult.assets.length > 0) {
  const typefaceAsset = typefaceResult.assets[0];
  const typeface = typefaceAsset.payload?.typeface;
  if (typeface && typeface.fonts?.[0]?.uri) {
    engine.block.setFont(textBlock, typeface.fonts[0].uri, typeface);
  }
}

Adding Visual Effects#

We add a glowing drop shadow effect for the neon look. Drop shadow creates the characteristic glow effect that makes caption presets visually distinctive:

// Add a glowing drop shadow effect for the neon look
// This creates the characteristic neon glow effect
engine.block.setDropShadowEnabled(textBlock, true);

// Set glow color (bright cyan to match text)
engine.block.setColor(textBlock, 'dropShadow/color', {
  r: 0.0,
  g: 1.0,
  b: 1.0,
  a: 0.8
});

// Configure shadow properties for a soft glow
engine.block.setFloat(textBlock, 'dropShadow/blurRadius/x', 20);
engine.block.setFloat(textBlock, 'dropShadow/blurRadius/y', 20);
engine.block.setFloat(textBlock, 'dropShadow/offset/x', 0);
engine.block.setFloat(textBlock, 'dropShadow/offset/y', 0);

Optionally, we add a semi-transparent background to help the caption stand out against video content:

// Optionally add a semi-transparent dark background
// This helps the caption stand out against video content
engine.block.setBackgroundColorEnabled(textBlock, true);
engine.block.setColor(textBlock, 'backgroundColor/color', {
  r: 0.0,
  g: 0.0,
  b: 0.1,
  a: 0.7
});

Serializing the Preset#

We serialize the styled text block using block.saveToString(). This creates a serialized string that can be saved as a .preset or .blocks file:

// Serialize the styled text block to create a preset file
// This serialized string can be saved as a .blocks or .preset file
// Include 'bundle' scheme to allow serialization of blocks with bundled fonts
const serializedPreset = await engine.block.saveToString(
  [textBlock],
  ['buffer', 'http', 'https', 'bundle']
);

console.log('=== Serialized Preset ===');
console.log('Save this as a .preset file (e.g., neon-glow.preset):');
console.log(serializedPreset);

The serialized string contains all block properties and styling. Save this output as a file (e.g., neon-glow.preset) and create a thumbnail image showing the preset appearance.

Defining Customizable Properties#

Color Properties#

We define which properties users can customize without changing the entire preset. Color properties allow users to modify specific color aspects of a preset:

// Example content.json entry for the custom preset
// This shows the structure needed to add the preset to content.json
const contentJsonEntry = {
  id: '//ly.img.captionPresets/neon-glow',
  label: {
    en: 'Neon Glow'
  },
  meta: {
    uri: '{{base_url}}/ly.img.captionPresets/presets/neon-glow.preset',
    thumbUri: '{{base_url}}/ly.img.captionPresets/thumbnails/neon-glow.png',
    mimeType: 'application/ubq-blocks-string'
  },
  payload: {
    properties: [
      {
        type: 'Color',
        property: 'fill/solid/color',
        value: { r: 0.0, g: 1.0, b: 1.0, a: 1.0 },
        defaultValue: { r: 0.0, g: 1.0, b: 1.0, a: 1.0 }
      },
      {
        type: 'Color',
        property: 'dropShadow/color',
        value: { r: 0.0, g: 1.0, b: 1.0, a: 0.8 },
        defaultValue: { r: 0.0, g: 1.0, b: 1.0, a: 0.8 }
      },
      {
        type: 'Color',
        property: 'backgroundColor/color',
        value: { r: 0.0, g: 0.0, b: 0.1, a: 0.7 },
        defaultValue: { r: 0.0, g: 0.0, b: 0.1, a: 0.7 }
      }
    ]
  }
};

console.log('\n=== content.json Entry ===');
console.log('Add this entry to your content.json assets array:');
console.log(JSON.stringify(contentJsonEntry, null, 2));

Each property in the payload.properties array needs:

type: Must be "Color" for color properties
property: Property path (e.g., "fill/solid/color", "backgroundColor/color", "dropShadow/color")
value: Current RGBA color object with r, g, b, a values (0-1 range)
defaultValue: Initial RGBA color object

Supported Property Paths#

Available property paths for caption customization:

fill/solid/color: Text fill color
backgroundColor/color: Background color behind text
dropShadow/color: Drop shadow color
stroke/color: Stroke/outline color

Updating the content.json File#

Adding a New Preset Entry#

Add a new object to the assets array with all required fields. The complete structure for a preset entry:

{
  "id": "//ly.img.captionPresets/neon-glow",
  "label": { "en": "Neon Glow" },
  "meta": {
    "uri": "{{base_url}}/ly.img.captionPresets/presets/neon-glow.preset",
    "thumbUri": "{{base_url}}/ly.img.captionPresets/thumbnails/neon-glow.png",
    "mimeType": "application/ubq-blocks-string"
  },
  "payload": {
    "properties": [
      {
        "type": "Color",
        "property": "fill/solid/color",
        "value": { "r": 0.0, "g": 1.0, "b": 1.0, "a": 1.0 },
        "defaultValue": { "r": 0.0, "g": 1.0, "b": 1.0, "a": 1.0 }
      },
      {
        "type": "Color",
        "property": "dropShadow/color",
        "value": { "r": 0.0, "g": 1.0, "b": 1.0, "a": 0.8 },
        "defaultValue": { "r": 0.0, "g": 1.0, "b": 1.0, "a": 0.8 }
      }
    ]
  }
}

Ensure the mimeType is set to "application/ubq-blocks-string" and use the {{base_url}} placeholder for dynamic path resolution.

Complete content.json Example#

The complete content.json file structure wraps preset entries in the assets array:

// Example of a complete content.json file structure
const completeContentJson = {
  version: '3.0.0',
  id: 'ly.img.captionPresets',
  assets: [contentJsonEntry]
};

console.log('\n=== Complete content.json Example ===');
console.log(JSON.stringify(completeContentJson, null, 2));

Hosting and Serving Custom Presets#

Server Setup#

Prepare the folder structure and upload files to your server:

Create folder structure matching assets/v4/ly.img.captionPresets/
Upload content.json to the root folder
Upload .preset files to presets/ subfolder
Upload thumbnail images to thumbnails/ subfolder
Ensure files are accessible via HTTP/HTTPS
Configure CORS headers if serving cross-origin

Verifying File Access#

Test that all files are accessible before configuring CE.SDK:

Access content.json directly in browser
Access preset files and thumbnails via their URLs
Check browser console for CORS errors

Loading Custom Presets into CE.SDK#

Base URL Configuration#

Set the base URL to point to your asset hosting location. CE.SDK automatically looks for ly.img.captionPresets/content.json relative to the base URL:

const config = {
  baseURL: 'https://your-server.com/assets/'
};

CreativeEditorSDK.create('#cesdk_container', config).then(async (cesdk) => {
  // Caption presets load automatically from baseURL + 'ly.img.captionPresets/content.json'
});

Your custom presets will seamlessly integrate with any built-in presets and automatically appear in the caption presets panel in the UI. No additional source registration is needed when replacing the default presets.

Troubleshooting#

Preset Not Loading#

Verify content.json is accessible at expected URL
Check browser console for 404 errors on preset files
Ensure mimeType is set to "application/ubq-blocks-string"
Verify {{base_url}} placeholder is used correctly

Preset Styles Not Applying#

Ensure preset was serialized from a text block (not other block types)
Verify the serialized block contains styling properties
Check that property paths in payload.properties are correct

Thumbnail Not Displaying#

Verify thumbnail file exists at the thumbUri path
Check image format is PNG
Ensure CORS headers allow image loading

Custom Colors Not Working#

Verify properties array structure in content.json
Check property type is "Color"
Ensure value and defaultValue have correct RGBA format (0-1 range)

API Reference#

Method	Category	Purpose
`engine.block.create('text')`	Block	Create text block for preset styling
`engine.block.saveToString(blocks)`	Block	Serialize styled block to preset format
`engine.block.setColor(id, property, color)`	Block	Set color property (fill, background, etc.)
`engine.block.setBackgroundColorEnabled()`	Block	Enable background color
`engine.block.setDropShadowEnabled()`	Block	Enable drop shadow
`engine.block.setFloat(id, property, value)`	Block	Set numeric properties (font size, etc.)
`engine.block.setString(id, property, val)`	Block	Set string properties (text, font URI)
`engine.asset.findAssets(sourceId, query)`	Asset	Find assets like typefaces
`CreativeEngine.init(config)`	Engine	Initialize engine with base URL config