Extract Moves From Video

Extract Moves from Video

This skill provides structured guidance for extracting text-based commands or moves from video recordings, particularly for text-based games, terminal sessions, or any screen recording where typed inputs need to be recovered.

When to Use This Skill

This skill applies when:

• Extracting game commands from recordings of text-based games (Zork, interactive fiction, MUDs)
• Recovering typed inputs from terminal session recordings
• Extracting user commands from any screen recording where text input is visible
• OCR-based extraction of sequential text entries from video

Strategic Approach

Phase 1: Environment Assessment

Before processing, assess the available tools and estimate resource requirements:

1. Check available tools in one comprehensive sweep:

   • FFmpeg for frame extraction
   • OCR engines (tesseract, pytesseract)
   • Image processing libraries (opencv-python, Pillow)
   • Python environment and package managers (pip, uv, conda)

2. Analyze video characteristics:

   • Duration and frame rate
   • Resolution and text clarity
   • Location of command input area (typically fixed position)
   • Text color contrast against background

3. Estimate processing time:

   • Benchmark OCR on 3-5 sample frames before full processing
   • Calculate expected total time based on frame count and benchmark

Phase 2: Region of Interest (ROI) Identification

Critical optimization: Identify and crop to the command input region before OCR.

For text-based games like Zork:

• Command input typically appears at a fixed screen location (often bottom)
• Command prompts have consistent markers (e.g., > prefix)
• Cropping to ROI dramatically improves OCR accuracy and speed

To identify the ROI:

1. Extract a few sample frames where commands are visible
2. Manually or programmatically identify the bounding box of the input area
3. Apply consistent cropping to all frames before OCR

Phase 3: Frame Extraction Strategy

Select frame extraction rate based on content characteristics:

• Text-based games: Commands persist on screen for seconds; 1-3 second intervals typically suffice
• Fast-paced inputs: May require higher frequency (0.5 second intervals)
• Start conservative: Begin with lower frequency, increase only if commands are missed

# Example: Extract frames at 1 frame per second
ffmpeg -i video.mp4 -vf "fps=1" frames/frame_%04d.png

Phase 4: OCR Preprocessing

Apply preprocessing to improve OCR accuracy:

1. Convert to grayscale
2. Apply thresholding (binary threshold for high contrast text)
3. Consider additional techniques if needed:
   • Contrast enhancement
   • Noise reduction
   • Dilation/erosion for text clarity
   • Inversion if text is light on dark background

See references/ocr_video_processing.md for detailed preprocessing techniques.

Phase 5: Domain-Aware Extraction and Validation

Key insight: Use domain knowledge to validate and correct OCR results.

For text-based games:

1. Obtain or construct a list of valid commands for the game
2. Use command vocabulary for spell-checking OCR output
3. Identify command syntax patterns (e.g., VERB NOUN, DIRECTION)
4. Flag entries that don't match known patterns for manual review

Common Zork-style commands include:

• Directions: n, s, e, w, ne, nw, se, sw, up, down
• Actions: get, take, drop, put, open, close, read, examine, look, inventory
• Combinations: get lamp, put sword in case, open mailbox

Phase 6: Deduplication and Cleaning

Handle duplicates arising from:

• Same command captured across multiple frames
• OCR variations of the same command (e.g., "get lamp" vs "get 1amp")

Deduplication strategy:

1. Normalize whitespace and case
2. Use fuzzy matching to group similar entries
3. When OCR variations exist, prefer the version matching known vocabulary
4. Remove incomplete/partial commands (single letters that aren't valid directions)

Phase 7: Validation

Before finalizing, validate the extracted command list:

1. Syntax validation: Verify commands match expected patterns
2. Sequence plausibility: Check that command order makes logical sense
3. Coverage check: Estimate if extracted count matches expected (based on video length)
4. Interpreter testing (if available): Run commands through a game interpreter to verify validity

Common Pitfalls

1. Skipping ROI extraction: Processing full frames wastes time and reduces accuracy
2. Inadequate preprocessing: Raw frames often need contrast/threshold adjustments
3. Ignoring domain knowledge: Valid command vocabulary enables validation and correction
4. Ad-hoc cleaning scripts: Design one robust cleaning pipeline rather than multiple iterations
5. No early validation: Test on sample frames before processing entire video
6. Timeout misestimation: Benchmark before committing to full processing
7. Capturing game output as commands: Filter to only lines with command prompt markers

Verification Checklist

• ROI identified and applied to frame extraction
• Preprocessing parameters tested on sample frames
• OCR benchmarked for time estimation
• Domain vocabulary used for validation
• Duplicates and near-duplicates removed
• Output validated against expected command syntax
• Command count reasonable for video duration