video-to-grayscale-frames

Video to Grayscale Frames

This skill guides you through extracting keyframes from MP4 video files and converting them to grayscale images for analysis.

Overview

The workflow has two main steps:

1. Extract keyframes from the MP4 video using FFmpeg
2. Convert to grayscale and save frames as PNG files

Step 1: Extract Keyframes from MP4

Use the ffmpeg skill to extract I-frames (keyframes) from the video.

Command Structure

ffmpeg -i <input.mp4> -vf "select=eq(pict_type\,I)" -vsync vfr <output_pattern>

Parameters

• input.mp4: Path to your video file
• output_pattern: Output file pattern (e.g., /root/keyframes_%03d.png)
  • %03d creates zero-padded numbers: keyframes_001.png, keyframes_002.png, etc.

Example

For a video at /root/super-mario.mp4, extracting to /root/keyframes_%03d.png:

ffmpeg -i /root/super-mario.mp4 -vf "select=eq(pict_type\,I)" -vsync vfr /root/keyframes_%03d.png

This creates: keyframes_001.png, keyframes_002.png, keyframes_003.png, etc.

Step 2: Convert Extracted Frames to Grayscale

Use the image_editing skill to convert each extracted keyframe to grayscale IN-PLACE (overwriting the original RGB image).

Conversion Process

For each keyframe image:

• Input: /root/keyframes_001.png (RGB)
• Operation: Convert to grayscale
• Output: /root/keyframes_001.png (grayscale, overwrites original)

Batch Processing

When converting multiple frames, process them sequentially or in parallel depending on available resources. Ensure each frame is converted and saved before proceeding to analysis.

Output Format

After this skill completes:

• Keyframes are stored as /root/keyframes_001.png, /root/keyframes_002.png, etc.
• All files are in grayscale format
• Files are ready for object detection and counting

Common Issues

• FFmpeg not installed: The ffmpeg skill should handle installation
• No keyframes extracted: Video may have no I-frames; consider extracting all frames with -fps 1 instead
• Image format errors: Ensure images are valid PNG files before grayscale conversion