@vocasync/astro

Turn your Astro blog posts into narrated audio with word-level synchronization.

Features

• 🎙️ Text-to-Speech Synthesis - Generate natural-sounding audio narration for your content
• 🎯 Word-Level Alignment - Precise timestamps for every word, powered by forced alignment
• ✨ Live Word Highlighting - Karaoke-style highlighting that follows along with playback
• 🎛️ Built-in Audio Player - Accessible player with keyboard shortcuts and mini-player mode
• 🌍 14 Languages - Global reach with support for 14 languages
• 🎨 Fully Themeable - CSS variables for seamless integration with any design

Demo

🔗 Live Demo — See the audio player and word highlighting in action

📂 Demo Source Code — Example implementation for reference

Table of Contents

• Installation
• Quick Start
• Project Structure
• Configuration
• CLI Commands
• Components
• Supported Languages
• Math Support
• Deployment
• Important: Audio Map
• Customizing Styles

Installation

npm install @vocasync/astro
# or
bun add @vocasync/astro
# or
pnpm add @vocasync/astro

Quick Start

1. Create VocaSync Config

Create a vocasync.config.mjs file in your project root:

// vocasync.config.mjs
export default {
  collection: {
    name: "blog",              // Your content collection name
    path: "./src/content/blog", // Path to your content
  },
};

2. Add to Astro Config

Update your astro.config.mjs:

// astro.config.mjs
import { defineConfig } from "astro/config";
import vocasync from "@vocasync/astro";
import { rehypeAudioWords } from "@vocasync/astro/rehype";

export default defineConfig({
  markdown: {
    rehypePlugins: [
      [rehypeAudioWords, {
        collectionName: "blog",                    // Must match your collection name
        audioMapPath: "src/data/audio-map.json"   // Must match output.audioMapPath
      }]
    ]
  },
  integrations: [vocasync()],
});

3. Set API Key

Create a .env file:

VOCASYNC_API_KEY=voca_xxxxxxxxxxxxxxxx

Get your API key at vocasync.io

4. Create Audio Map Directory

mkdir -p src/data

5. Sync Your Content

npx vocasync sync

This will, for each post:

• Read the content from your collection
• Submit a synthesis job, then an explicit alignment job (with the post's transcript)
• Wait for both to complete and fetch the word timings
• Save everything (URLs, keys, timings) to audio-map.json

6. Add the Player Component

In your article layout or page:

---
// src/layouts/ArticleLayout.astro
import AudioPlayer from "@vocasync/astro/components/AudioPlayer.astro";
import audioMap from "../data/audio-map.json";

const { post } = Astro.props;
const audioEntry = audioMap.entries[post.slug];
---

<article>
  <!-- Audio player at the top -->
  <AudioPlayer slug={post.slug} audioEntry={audioEntry} label="Listen to this post" />
  
  <!-- Article content - must have data-article-body for word highlighting -->
  <div data-article-body>
    <slot />
  </div>
</article>

Project Structure

After setup, your project should look like this:

my-astro-site/
├── astro.config.mjs          # Astro config with vocasync integration
├── vocasync.config.mjs       # VocaSync configuration
├── .env                      # API key (add to .gitignore)
├── src/
│   ├── content/
│   │   └── blog/             # Your content collection
│   │       ├── my-post.md
│   │       └── another-post.md
│   ├── data/
│   │   └── audio-map.json    # Generated - DO NOT DELETE (see below)
│   └── layouts/
│       └── ArticleLayout.astro
└── package.json

Configuration

vocasync.config.mjs

Full configuration options:

// vocasync.config.mjs
export default {
  // Content collection settings (required)
  collection: {
    name: "blog",                    // Collection name
    path: "./src/content/blog",      // Path to content files
    slugField: "slug",               // Frontmatter field for slug (optional)
  },
  
  // Language for synthesis and alignment (ISO 639-1 code)
  // See "Supported Languages" section below for all options
  language: "en",
  
  // Synthesis settings
  synthesis: {
    // alloy, ash, coral, echo, fable, onyx, nova, sage, shimmer
    voice: "onyx",
    quality: "sd",                   // sd (standard) or hd (high definition)
    format: "mp3",                   // mp3, aac, opus, flac, wav (sent as outputFormat)
  },
  
  // LaTeX/math support
  math: {
    enabled: false,                  // Enable math-to-speech conversion
    style: "clearspeak",             // clearspeak or mathspeak
  },
  
  // Output settings
  output: {
    audioMapPath: "./src/data/audio-map.json",
  },
  
  // Frontmatter field to opt-in/out per post
  frontmatterField: "audio",         // Set `audio: false` in frontmatter to skip
  
  // Processing options
  processing: {
    concurrency: 3,                  // Parallel jobs (1-10)
    force: false,                    // Force reprocessing
  },
};

Per-Post Overrides

Any post can override the global voice, language, or format from its frontmatter. Values that aren't overridden fall back to vocasync.config.mjs:

---
title: "Bienvenue"
language: fr
voice: shimmer
---

Bonjour…

Invalid values are skipped with a warning. Changing any of these re-syncs the post (the change-detection hash includes the resolved voice/language/format).

Rehype Plugin Options

// In astro.config.mjs
[rehypeAudioWords, {
  collectionName: "blog",                  // Content collection name
  audioMapPath: "src/data/audio-map.json", // Path to audio map
  classPrefix: "vocasync",                 // CSS class prefix (default: "vocasync")
}]

CLI Commands

# Sync all content (synthesis + alignment)
npx vocasync sync

# Sync a single post
npx vocasync sync --only my-post-slug

# Force reprocessing (ignores cache)
npx vocasync sync --force

# Dry run (preview without API calls)
npx vocasync sync --dry-run

# Use a custom config file
npx vocasync sync --config ./path/to/vocasync.config.mjs

# Check configuration
npx vocasync check

# Check job status
npx vocasync status <projectUuid>

# Show help
npx vocasync help

CLI Options

Option	Description
--only <slug>	Only process a specific post by slug
--force	Force reprocessing, ignore cache
--dry-run	Preview what would be processed without API calls
--config <path>	Use a custom config file path

Components

AudioPlayer

The main audio player component with word highlighting support.

---
import AudioPlayer from "@vocasync/astro/components/AudioPlayer.astro";
---

<AudioPlayer
  slug={post.slug}
  label="Listen to this post"
  articleSelector="[data-article-body]"
  enableHighlighting={true}
  enableClickToSeek={true}
  enableMiniPlayer={true}
  trailLength={4}
/>

Props

Prop	Type	Default	Description
slug	string	required	Post slug to lookup audio
audioEntry	object	undefined	Audio entry from audio-map.json (audioUrl, synthesisPublishableKey, words, duration)
label	string	"Listen to this article"	Accessible label
showPlaceholder	boolean	true	Show message when no audio
class	string	""	Additional CSS classes
articleSelector	string	"[data-article-body]"	Selector for word highlighting container
enableMiniPlayer	boolean	true	Show floating mini player on scroll
enableHighlighting	boolean	true	Enable word highlighting
enableClickToSeek	boolean	true	Enable click on words to seek audio
trailLength	number	4	Number of trailing highlighted words

Keyboard Shortcuts

When the player is focused (click on it or Tab to it), the following keyboard shortcuts are available:

Key	Action
Space	Play/Pause
← Left Arrow	Seek backward 5 seconds
→ Right Arrow	Seek forward 5 seconds
M	Toggle mute
H	Toggle word highlighting

Highlighting Toggle

The player includes a highlighter icon button that allows users to toggle word highlighting on/off during playback. This is useful for users who find the highlighting distracting or prefer to just listen.

Click-to-Seek

When enableClickToSeek is enabled (default), clicking on any word in the article will:

1. Seek the audio to that word's timestamp
2. Start playback if paused

This is useful for jumping to specific parts of an article. Disable it with enableClickToSeek={false} if you prefer words to not be interactive.

Word Highlighting

For word highlighting to work, wrap your article content with data-article-body:

<div data-article-body>
  <Content />  <!-- Your markdown content -->
</div>

The rehype plugin wraps each word in a <span> with timing data at build time.

Supported Languages

VocaSync supports 14 languages where both speech synthesis and forced alignment are available. Languages use ISO 639-1 codes:

Code	Language	Code	Language
zh	Chinese	pl	Polish
cs	Czech	pt	Portuguese
en	English	ru	Russian
fr	French	es	Spanish
de	German	sv	Swedish
ja	Japanese	tr	Turkish
ko	Korean	uk	Ukrainian

Note: VocaSync requires both speech synthesis and word-level forced alignment for each language. While synthesis (powered by OpenAI TTS) supports 61 languages, alignment (powered by Montreal Forced Aligner) is available for a smaller set. The 14 languages listed above are where both capabilities overlap, and they match the platform's alignment-supported set.

Math Support

VocaSync supports LaTeX math equations using Speech Rule Engine to convert math to spoken text.

Installation

Install the math dependencies. mathjax-full powers both the spoken form and (via rehype-mathjax) the visual rendering, so you don't also need KaTeX:

bun add remark-math rehype-mathjax mathjax-full speech-rule-engine

Setup

Math needs three plugins in a specific order:

// astro.config.mjs
import { defineConfig } from "astro/config";
import vocasync from "@vocasync/astro";
import { rehypeAudioWords, rehypeMathSpeech } from "@vocasync/astro/rehype";
import remarkMath from "remark-math";
import rehypeMathjax from "rehype-mathjax";

const collectionName = "blog";
const audioMapPath = "src/data/audio-map.json";

export default defineConfig({
  markdown: {
    remarkPlugins: [remarkMath], // parse $...$ / $$...$$
    rehypePlugins: [
      [rehypeMathSpeech, { collectionName, audioMapPath }], // attach spoken form (before render)
      rehypeMathjax,                                        // render math to HTML
      [rehypeAudioWords, { collectionName, audioMapPath }], // wrap words + math units
    ],
  },
  integrations: [vocasync()],
});

Enable math in vocasync.config.mjs so vocasync sync generates the spoken forms:

export default {
  // ...
  math: { enabled: true, style: "clearspeak" }, // or "mathspeak"
};

Currency $ collides with math. With remark-math enabled, $5 … $1200 is parsed as an inline math span. Escape currency dollar signs as \$ (e.g. \$5, \$1200) so they're treated as text — VocaSync then speaks them correctly ("five dollars").

How It Works

1. During vocasync sync (Node/CLI), each LaTeX expression is converted to spoken text (e.g. $x^2$ → "x squared") and stored in audio-map.json. It's spoken and aligned as part of the post's audio.
2. At build time, rehypeMathSpeech reads those spoken forms from the audio map and attaches each as a data-speech attribute on the math element (math-to-speech never runs inside the Astro/Vite build).
3. rehypeMathjax renders the math to visual HTML.
4. rehypeAudioWords wraps each math expression as a single highlight unit, so the whole equation lights up together while it's read.

Configuration

Set the speech style in vocasync.config.mjs:

export default {
  // ...
  math: {
    enabled: true,
    style: "clearspeak",  // or "mathspeak"
  },
};

• clearspeak: Natural, conversational style (recommended)
• mathspeak: More formal, precise mathematical speech

Deployment

Build Strategy

For Large Content Collections

If you have many posts, we recommend running npx vocasync sync once locally before your first deployment:

# Run locally to generate all audio (may take a while)
npx vocasync sync

# Commit the audio-map to version control
git add src/data/audio-map.json
git commit -m "Add audio map"
git push

This approach:

• Prevents long CI/CD build times (important for platforms like Vercel with time limits)
• Only new or changed posts will be processed on subsequent builds
• Audio map acts as a cache - existing entries are skipped

For New/Updated Posts

For ongoing updates, include the sync command in your build script:

{
  "scripts": {
    "dev": "astro dev",
    "build": "npx vocasync sync && astro build",
    "preview": "astro preview"
  }
}

Since most builds only process new or changed content, this adds minimal time.

CI/CD Environment Variables

Make sure to set VOCASYNC_API_KEY in your deployment environment:

• Vercel: Settings → Environment Variables
• Netlify: Site settings → Environment variables
• GitHub Actions: Repository secrets

Example GitHub Actions

name: Deploy
on:
  push:
    branches: [main]

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: oven-sh/setup-bun@v1
      
      - run: bun install
      - run: bun run build
        env:
          VOCASYNC_API_KEY: ${{ secrets.VOCASYNC_API_KEY }}
      
      - name: Deploy
        # Your deploy step here

Important: Audio Map

What is audio-map.json?

The audio-map.json file is the source of truth for VocaSync. Each entry stores:

• The synthesis and alignment project UUIDs (the two-POST flow uses two projects)
• A publishable key for each (the synthesis key streams the audio; the alignment key was used at build time to fetch the timings)
• The word timings (words) and any math spoken forms (mathSpeech), embedded so the player needs no runtime alignment fetch
• The resolved voice / language / format, a content hash, and timestamps

Audio Map Versions

• Version 1/2 (legacy): a single project + one publishableKey, no embedded timings.
• Version 3 (current): two projects + two publishable keys, embedded words timings, and per-post voice/language/format.

Legacy v1/v2 entries are missing the v3 fields, so the first vocasync sync re-synthesizes them once to produce complete v3 entries.

⚠️ Do Not Delete

If you delete audio-map.json, running npx vocasync sync will re-create synthesis and alignment jobs for ALL content. This will:

1. Incur API costs for re-processing everything
2. Generate new audio files (old URLs will still work)

Best Practices

1. Commit to version control: Add audio-map.json to git
2. Back it up: Keep a backup before major changes
3. Don't edit manually: Let the CLI manage this file

# Add to git
git add src/data/audio-map.json
git commit -m "Add audio map"

What to Ignore

Add your .env file to .gitignore:

# .gitignore
.env
.env.local

Customizing Styles

Override CSS variables to match your theme:

:root {
  /* Player colors */
  --vocasync-primary: #3b82f6;
  --vocasync-primary-content: white;
  --vocasync-surface: #f8fafc;
  --vocasync-border: #e2e8f0;
  --vocasync-text: #1e293b;
  --vocasync-text-muted: #64748b;
  
  /* Word highlighting */
  --vocasync-highlight: #10b981;
  --vocasync-highlight-text: white;
  --vocasync-highlight-active-opacity: 0.25;
  --vocasync-highlight-trail-opacity: 0.12;
}

/* Dark mode */
@media (prefers-color-scheme: dark) {
  :root {
    --vocasync-surface: #1e293b;
    --vocasync-border: #334155;
    --vocasync-text: #f1f5f9;
    --vocasync-text-muted: #94a3b8;
  }
}

Troubleshooting

"No VocaSync configuration found"

Create a vocasync.config.mjs file in your project root.

Words not highlighting

1. Make sure the rehype plugin is configured in astro.config.mjs
2. Check that collectionName matches your collection
3. Verify audioMapPath points to your audio map
4. Ensure content is wrapped in [data-article-body]

Audio not playing

1. Run npx vocasync sync to generate audio
2. Check that audio-map.json exists and has entries
3. Verify the slug prop matches your content slug

CLI errors

# Check your configuration
npx vocasync check

# Verify API key is set
echo $VOCASYNC_API_KEY

License

MIT