I've created a command-line tool called subscan that does exactly what you're looking for. It combines all the steps you mentioned into a single pipeline:

1. Crop video to subtitle area
2. Extract frames at specified frame rate
3. OCR the frames (using Apple's Vision framework for better accuracy)
4. Remove duplicates and empty lines

Here's how to use it:

# Install via Homebrew
brew tap vangie/formula
brew install subscan

# Basic usage (read from file)
subscan -i video.mp4 -a 600x50+210+498 -o subtitles.txt

# Using pipe with custom frame rate (2 fps)
cat video.mp4 | subscan -a 600x50+210+498 -r 2 > subs.txt

# Use fast mode with specific languages
subscan -i video.mp4 -a 600x50+210+498 -f -l "en-US,zh-CN" -o subs.txt

Key features:

• Supports any video format that ffmpeg can handle
• Uses Apple's Vision framework for accurate OCR
• Supports multiple languages
• Adjustable frame rate for balancing accuracy and speed
• Pipeline support for flexible video processing

The tool is open source and available at: https://github.com/vangie/subscan

Requirements:

• macOS 10.15 (Catalina) or later
• ffmpeg (automatically installed by Homebrew)