# Transcript-Based EPUB3 System - Implementation Summary

## ✅ Completed Implementation

### 1. Transcript JSON Schema & Model ✅

**File:** `backend/src/models/Transcript.js`

- **Purpose**: File-based storage for transcript JSON files
- **Location**: `backend/transcripts/job_{jobId}/chapter_{pageNumber}.json`
- **Features**:
  - Schema validation
  - CRUD operations
  - Text file generation for aeneas
  - Directory management

**Key Methods:**
- `loadTranscript(jobId, pageNumber)` - Load transcript JSON
- `saveTranscript(jobId, pageNumber, transcriptData)` - Save transcript JSON
- `saveTextFile(jobId, pageNumber, text)` - Save plain text for aeneas
- `generateTextForAeneas(transcriptData)` - Generate text file content
- `validateTranscriptSchema(transcriptData)` - Validate schema

### 2. Transcript Service ✅

**File:** `backend/src/services/transcriptService.js`

- **Purpose**: Business logic for transcript management
- **Features**:
  - Initialize transcript from sync data
  - Update fragment text (single & batch)
  - Re-run aeneas alignment
  - Get transcript for editing

**Key Methods:**
- `initializeFromSyncData()` - Create transcript from existing sync data
- `updateFragmentText()` - Update single fragment text
- `updateFragmentTexts()` - Batch update fragment texts
- `realignTranscript()` - Re-run aeneas with edited text
- `getTranscriptForEditing()` - Get transcript formatted for UI

### 3. Aeneas Integration ✅

**Integration:** Uses existing `aeneasService.js`

- **Flow**:
  1. Generate plain text file from transcript
  2. Execute aeneas: `audio.mp3 + text.txt → alignment.json`
  3. Map aeneas fragments back to transcript fragments
  4. Update transcript with new timings (preserve IDs and text)

**Key Points:**
- Fragment IDs are preserved during realignment
- Text content comes from transcript (edited text)
- Only timings are updated from aeneas output

### 4. SMIL Generator ✅

**File:** `backend/src/services/smilGenerator.js`

- **Purpose**: Generate EPUB3-compliant SMIL from transcript
- **Output**: SMIL XML with `<par>` elements for each fragment
- **Features**:
  - Fragment IDs match XHTML IDs exactly
  - Audio clipBegin/clipEnd from transcript timings
  - EPUB3-compliant structure

**Key Functions:**
- `generateSMILFromTranscript()` - Generate SMIL XML
- `generateAndSaveSMIL()` - Generate and save SMIL file

**SMIL Structure:**
```xml
<smil>
  <body>
    <seq>
      <par>
        <text src="page_1.xhtml#fragmentId"/>
        <audio src="audio.mp3" clipBegin="0.000s" clipEnd="2.345s"/>
      </par>
    </seq>
  </body>
</smil>
```

### 5. XHTML Generator ✅

**File:** `backend/src/services/xhtmlGenerator.js`

- **Purpose**: Generate EPUB3-compliant XHTML from transcript
- **Output**: XHTML with elements matching fragment IDs
- **Features**:
  - Fragment IDs as element IDs
  - Text content from transcript
  - Media overlay CSS classes
  - Semantic HTML structure

**Key Functions:**
- `generateXHTMLFromTranscript()` - Generate XHTML
- `generateSemanticXHTMLFromTranscript()` - Generate with semantic structure
- `generateAndSaveXHTML()` - Generate and save XHTML file

**XHTML Structure:**
```xml
<html>
  <body>
    <p id="fragmentId" class="epub-media-overlay-active">text content</p>
  </body>
</html>
```

### 6. EPUB Builder ✅

**File:** `backend/src/services/epubBuilderFromTranscript.js`

- **Purpose**: Build complete EPUB3 package from transcripts
- **Features**:
  - Loads all transcripts for a job
  - Generates XHTML files
  - Generates SMIL files
  - Builds OPF manifest with media overlay references
  - Packages EPUB3 file

**Key Methods:**
- `build()` - Main build function
- `generateXHTMLFiles()` - Generate all XHTML files
- `generateSMILFiles()` - Generate all SMIL files
- `generateOPF()` - Generate OPF manifest
- `packageEpub()` - Package EPUB file

### 7. API Routes ✅

**File:** `backend/src/routes/transcriptRoutes.js`

**Endpoints:**
- `GET /api/transcripts/job/:jobId` - List all transcripts
- `GET /api/transcripts/job/:jobId/page/:pageNumber` - Get transcript
- `PUT /api/transcripts/job/:jobId/page/:pageNumber/fragment/:fragmentId` - Update text
- `PUT /api/transcripts/job/:jobId/page/:pageNumber/fragments` - Batch update
- `POST /api/transcripts/job/:jobId/page/:pageNumber/realign` - Re-run aeneas
- `POST /api/transcripts/job/:jobId/initialize` - Initialize from sync data
- `POST /api/transcripts/job/:jobId/build-epub` - Build EPUB

### 8. Server Integration ✅

**File:** `backend/server.js`

- Added transcript routes to Express app
- Routes available at `/api/transcripts/*`

## File Structure

```
backend/
├── transcripts/                    # Transcript storage
│   ├── job_123/
│   │   ├── chapter_1.json        # Transcript JSON
│   │   ├── chapter_1.txt         # Plain text for aeneas
│   │   └── chapter_2.json
│   ├── ARCHITECTURE.md           # Architecture docs
│   ├── EXAMPLES.md               # Usage examples
│   ├── MIGRATION_GUIDE.md        # Migration guide
│   └── sample_chapter_1.json     # Sample transcript
│
├── src/
│   ├── models/
│   │   └── Transcript.js         # Transcript model
│   │
│   ├── services/
│   │   ├── transcriptService.js           # Transcript service
│   │   ├── smilGenerator.js               # SMIL generator
│   │   ├── xhtmlGenerator.js              # XHTML generator
│   │   └── epubBuilderFromTranscript.js   # EPUB builder
│   │
│   └── routes/
│       └── transcriptRoutes.js    # API routes
```

## Workflow Diagram

```
┌─────────────────────────────────────────────────────────────┐
│ 1. USER EDITS TEXT                                         │
│    PUT /api/transcripts/job/123/page/1/fragment/id        │
│    { "text": "edited text" }                               │
└────────────────────┬──────────────────────────────────────┘
                     │
                     ▼
┌─────────────────────────────────────────────────────────────┐
│ 2. TRANSCRIPT JSON UPDATED                                   │
│    chapter_1.json: { fragments: [{ id, text: "edited" }] } │
└────────────────────┬──────────────────────────────────────┘
                     │
                     ▼
┌─────────────────────────────────────────────────────────────┐
│ 3. RE-RUN AENEAS                                            │
│    POST /api/transcripts/job/123/page/1/realign            │
│    → Generates chapter_1.txt                                │
│    → Runs: aeneas audio.mp3 chapter_1.txt → alignment.json │
│    → Updates transcript with new timings                    │
└────────────────────┬──────────────────────────────────────┘
                     │
                     ▼
┌─────────────────────────────────────────────────────────────┐
│ 4. GENERATE EPUB                                            │
│    POST /api/transcripts/job/123/build-epub                │
│    → Loads all transcripts                                  │
│    → Generates XHTML from transcripts                       │
│    → Generates SMIL from transcripts                        │
│    → Builds OPF manifest                                    │
│    → Packages EPUB3 file                                    │
└─────────────────────────────────────────────────────────────┘
```

## Key Design Decisions

### 1. Why Transcript JSON?

- **Single Source of Truth**: All content and timings in one place
- **Human Readable**: Easy to debug and edit
- **Version Control**: Can be tracked in git
- **Offline Editing**: Can edit without database connection

### 2. Why File-Based Storage?

- **Simplicity**: No database schema changes needed
- **Performance**: Fast file I/O
- **Portability**: Easy to backup/restore
- **Flexibility**: Can add metadata without schema changes

### 3. Why Re-run Aeneas After Editing?

- **Accuracy**: Edited text may have different duration
- **Consistency**: All timings come from aeneas
- **Quality**: Ensures proper alignment

### 4. Why Generate XHTML/SMIL from Transcript?

- **Consistency**: Same source = same output
- **Maintainability**: One place to fix bugs
- **Reliability**: No manual editing = no errors

## Testing Checklist

- [ ] Initialize transcript from sync data
- [ ] Edit single fragment text
- [ ] Batch edit multiple fragments
- [ ] Re-run aeneas alignment
- [ ] Verify transcript updated with new timings
- [ ] Generate SMIL file
- [ ] Verify SMIL references match XHTML IDs
- [ ] Generate XHTML file
- [ ] Verify XHTML IDs match transcript fragment IDs
- [ ] Build EPUB package
- [ ] Verify EPUB opens in reader
- [ ] Verify media overlay highlighting works
- [ ] Verify audio playback matches text

## Next Steps

1. **Frontend Integration**: Update UI to use transcript API
2. **Migration Script**: Create automated migration tool
3. **Testing**: Comprehensive testing with real data
4. **Documentation**: User guide for editing workflow
5. **Performance**: Optimize for large books (300+ pages)

## Production Considerations

1. **Backup**: Regular backups of transcript directories
2. **Monitoring**: Log transcript operations
3. **Error Handling**: Graceful handling of aeneas failures
4. **Validation**: Strict schema validation
5. **Performance**: Cache transcripts in memory for large jobs

## Support

For questions or issues:
- See `ARCHITECTURE.md` for architecture details
- See `EXAMPLES.md` for usage examples
- See `MIGRATION_GUIDE.md` for migration steps