SRT Translator

A powerful, browser-based tool for translating SRT subtitle files using AI. Built for speed, accuracy, and ease of use.

🎯 What Problem Does It Solve?

Translating subtitles is tedious and expensive:

• Manual translation is slow and costly
• Generic AI translation loses subtitle timing and structure
• Existing tools don't handle the unique challenges of SRT format (split sentences, timing markers, etc.)

SRT Translator solves this by:

1. Preserving all timestamps exactly as-is
2. Using a smart marker system to maintain line-by-line correspondence
3. Processing chunks in parallel for maximum speed
4. Allowing custom instructions for domain-specific terminology

✨ Features

• Drag & Drop - Just drop your SRT file and go
• 100 Parallel Requests - Blazing fast translation
• Smart Chunking - Processes 20 subtitle blocks per request for optimal precision
• Marker-Based Alignment - Each subtitle block stays aligned with its timestamp
• Custom Instructions - Add context-specific translation rules (e.g., "Use informal 'sen' instead of formal 'siz'")
• Custom Model Support - Use any model available on OpenRouter
• Multi-Language - Translate to 15+ popular languages
• Real-Time Progress - Visual feedback for each chunk's status
• Retry with Backoff - Automatic retry on failures

🚀 Quick Start

1. Open index.html in your browser
2. Enter your OpenRouter API key
3. Drop an SRT file
4. Select target language
5. Click "Translate"
6. Download your translated SRT

⚙️ Configuration

Setting	Default	Description
Model	google/gemini-3-flash-preview	AI model for translation
Chunk Size	20	Number of subtitle blocks per API request
Parallel Requests	100	Maximum concurrent API calls

Recommended Settings

Chunk Size: 20 is recommended for better precision. Smaller chunks mean:

• Less text drift between subtitle blocks
• More accurate timing alignment
• Slightly more API calls, but with 100 parallel requests it's still fast

For the best performance/cost balance, we recommend:

google/gemini-3-flash-preview

This model offers:

• Fast response times
• Excellent instruction following
• Great translation quality
• Cost-effective pricing

Other options:

• google/gemini-2.5-flash-lite - Budget option, may have lower accuracy

🧠 How It Works

The Problem: Text Drift

Subtitles split sentences across multiple timed blocks. The problem? Languages have different structures.

English (SVO): "I love you" → Subject, Verb, Object
Turkish (SOV): "Seni seviyorum" → Object, Subject+Verb

When you translate subtitle blocks independently, the words end up in wrong timestamps:

English Subtitles:          Turkish (Naive Translation):
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
[00:01] "I will not"    →   [00:01] "Bunu yapmayacağım"  ← Too long!
[00:02] "do this."      →   [00:02] ""                    ← Empty!

The AI translated the full sentence in Block 1, leaving Block 2 empty. Now timing is broken.

The Solution: Markers

We inject [B#] markers to create explicit boundaries:

Input to AI:

[B1] Hello and welcome to
[B2] a new episode. Today we have
[B3] Chris Titus with us.

AI Output:

[B1] Merhaba ve yeni bir
[B2] bölüme hoş geldiniz. Bugün yanımızda
[B3] Chris Titus var.

Each marker acts as an anchor:

• [B1] content stays in Block 1's timestamp
• [B2] content stays in Block 2's timestamp
• Sentence boundaries can span blocks - that's fine!

Smart Chunking

Chunks don't break at fixed sizes. We look for natural sentence endings (. ! ?) within the last 10 blocks:

Target: 20 blocks
Actual: 23 blocks (because sentence ends at block 23)

Translation Priority

1. Line Structure (Mandatory) - Each [B#] stays on its own line
2. Natural Translation - Idiomatic, not word-for-word
3. Word Count (Soft) - Similar length per line when possible

📁 Project Structure

srt-translator/
├── index.html          # Main UI entry point
├── README.md           # Documentation
├── src/
│   ├── app.js          # Core application logic
│   └── styles.css      # Dark theme styling
└── assets/
    └── ui.webp         # UI screenshot

🔧 Custom Instructions Examples

Turkish informal:

Türkçe çeviride "siz" yerine "sen" formu kullan.

Technical content:

Keep technical terms like "API", "SDK", "cache" untranslated.

YouTube tone:

Use casual, engaging language suitable for YouTube videos.

📝 API Requirements

• Provider: OpenRouter
• API Key: Get one at https://openrouter.ai/keys
• Models: Any chat completion model on OpenRouter

🛡️ Privacy

• Your API key is stored locally in your browser (localStorage)
• SRT files are processed client-side
• Only subtitle text is sent to the AI API
• No data is stored on any server

📄 License

GPL-3.0 License

Built with ❤️ for content creators who need fast, accurate subtitle translations.