slidegeist 2025.10.24

Extract slides and transcripts from lecture videos with minimal dependencies

Slidegeist

Extract slides and timestamped transcripts from lecture videos with minimal dependencies.

Features

• Scene detection using global pixel difference (research-based method optimized for lecture videos)
• Automatic slide extraction with simple numbered filenames (slide_001, slide_002, ...)
• Audio transcription with Whisper large-v3 model (highest quality)
• MLX acceleration on Apple Silicon Macs for 2-3x faster transcription
• Markdown export - single slides.md file (LLM-friendly) or split mode with separate files
• OCR with refinement - Tesseract OCR with optional Qwen3-VL vision model enhancement

Requirements

• Python ≥ 3.10
• FFmpeg (must be installed separately and available in PATH)

Installing FFmpeg

macOS:

brew install ffmpeg

Ubuntu/Debian:

sudo apt-get install ffmpeg

Windows: Download from ffmpeg.org or use:

winget install ffmpeg

Installation

pip install slidegeist

• Apple Silicon users can get MLX acceleration with pip install "slidegeist[mlx]".
• Enable Whisper CUDA builds by installing PyTorch with CUDA before Slidegeist.

Developer Setup

git clone [e-mail]:itpplasma/slidegeist.git
cd slidegeist
pip install -e ".[dev]"

Quick Start

Process a lecture video to extract slides and transcript:

slidegeist lecture.mp4 --out output/

This creates:

output/
├── slides.md                        # Combined file with table of contents and all slides
└── slides/
    ├── slide_001.jpg                # Slide images (1-based numbering)
    ├── slide_002.jpg
    └── slide_003.jpg

For separate slide files (useful for navigation in some tools), use --split:

slidegeist lecture.mp4 --split

This creates:

output/
├── index.md                         # Overview with links to all slides
├── slide_001.md                     # Slide 1 with transcript and OCR
├── slide_002.md                     # Slide 2 with transcript and OCR
├── slide_003.md                     # Slide 3 with transcript and OCR
└── slides/
    ├── slide_001.jpg                # Slide images
    ├── slide_002.jpg
    └── slide_003.jpg

Usage

Full Processing

# Basic usage (auto-detects MLX on Apple Silicon, uses large-v3 model)
slidegeist video.mp4

# Specify output directory
slidegeist video.mp4 --out my-output/

# Use GPU explicitly (NVIDIA)
slidegeist video.mp4 --device cuda

# Use smaller/faster model
slidegeist video.mp4 --model base

# Adjust scene detection sensitivity (0.0-1.0, default 0.025).
# Acts as the *starting point* for the Opencast optimizer.
# Lower values bias toward more segments; higher values toward fewer.
slidegeist video.mp4 --scene-threshold 0.015

# Explicit process command (same as default)
slidegeist process video.mp4

Individual Operations

# Extract only slides (no transcription)
slidegeist slides video.mp4

CLI Options

slidegeist <video> [options]
slidegeist {process,slides} <video> [options]

Options:
  --out DIR              Output directory (default: video filename)
  --split               Create separate markdown files (index.md + slide_NNN.md)
                        instead of single slides.md (default: combined file)
  --scene-threshold NUM  Initial scene detection sensitivity 0.0-1.0 (default: 0.025)
                         Used as the optimizer's starting threshold; it will
                         auto-adjust to reach a stable segment count.
  --model NAME          Whisper model: tiny, base, small, medium, large, large-v2, large-v3
                        (default: large-v3)
  --device NAME         Device: cpu, cuda, or auto (default: auto)
                        auto = MLX on Apple Silicon if available, else CPU
  --format FMT          Image format: jpg or png (default: jpg)
  -v, --verbose         Enable verbose logging

Output Format

Default: Combined slides.md (Recommended)

By default, Slidegeist creates a single slides.md file containing:

• Video metadata (source, duration, model used)
• Table of contents with clickable links to each slide
• All slides with images, transcripts, and OCR content

Benefits:

• Single file is easy to process with LLMs
• No navigation between files needed
• Smaller overall output size

Example structure:

# Lecture Slides

**Video:** lecture.mp4
**Duration:** 45:30
**Transcription Model:** large-v3

## Table of Contents

- [Slide 1](#slide_001) • 00:00-05:15
- [Slide 2](#slide_002) • 05:15-12:30
...

---

## Slide 1

**Time:** 00:00 - 05:15

![Slide](slides/slide_001.jpg)

**Slide Content:**
Introduction to Quantum Mechanics

**Transcript:**
Today we discuss quantum mechanics and its implications...

---

## Slide 2
...

Split Mode (--split flag)

With --split, creates separate files for each slide (useful for some viewers/tools):

• Index: index.md - Overview with links to individual slide files
• Slide markdown: slide_001.md, slide_002.md, ... - Per-slide files with YAML front matter
• Slide images: slides/slide_001.jpg, slides/slide_002.jpg, ...

Each split slide file contains:

---
id: slide_001
index: 1
time_start: 0.0
time_end: 315.0
image: slides/slide_001.jpg
---

# Slide 1

[![Slide Image](slides/slide_001.jpg)](slides/slide_001.jpg)

## Transcript

Today we discuss quantum mechanics...

## Slide Content

Introduction to Quantum Mechanics

**Visual Elements:** diagram, formula

How It Works

1. Scene Detection: Uses FFmpeg's scene filter (SAD-based) with an Opencast-style optimizer to identify slide changes
   • Iteratively adjusts the scene threshold to target ~30 segments per hour (typical slide pace)
   • Treats --scene-threshold as the initial threshold; the optimizer raises or lowers it until the slide count converges
   • Merges segments shorter than 2 seconds to suppress rapid flickers
   • Based on Opencast's VideoSegmenterService implementation
2. Slide Extraction: Extracts frames at 80% through each segment into slides/ directory with simple slide_XXX.jpg names
3. Transcription: Uses Whisper large-v3 for state-of-the-art speech-to-text with timestamps
   • Auto-detects and uses MLX on Apple Silicon for 2-3x speedup
   • Falls back to faster-whisper on other platforms
4. OCR (optional): Uses Tesseract OCR with optional Qwen3-VL refinement (MLX only on Apple Silicon)
5. Export: Generates Markdown files with YAML front matter, linking slides to their transcripts and OCR content

Performance

Transcription Speed (Apple Silicon with MLX):

• 1 hour lecture: ~10-15 minutes (large-v3 model)
• Without MLX: ~25-35 minutes

Model Recommendations:

• large-v3: Best accuracy (default) - recommended for production
• medium: Good balance - 2x faster, slightly lower accuracy
• base: Quick testing - 5x faster, noticeably lower accuracy
• tiny: Very fast - 10x faster, lowest accuracy

Limitations

• Scene detection may need threshold tuning for some videos (default 0.025 works well for most lectures; because the optimizer auto-adjusts, use lower values like 0.015 to bias toward more slides or 0.03+ to bias toward fewer major transitions)

Advanced Threshold Tuning

• The Opencast optimizer targets roughly 30 segments per hour. That goal works well for standard lectures but you can steer it:
  • Lower --scene-threshold to encourage more segments before optimization. Useful when the optimizer consistently undershoots the actual slide count.
  • Raise --scene-threshold to bias toward fewer segments when the optimizer overshoots and splits slides too often.
• --scene-threshold is still bounded between 0.0 and 1.0. Values outside this range will be rejected by the CLI validator.
• No speaker diarization
• No automatic slide deduplication

Development

# Install with dev dependencies
pip install -e ".[dev]"

# Run tests
pytest

# Run linter
ruff check slidegeist/

# Run type checker
mypy slidegeist/

Legal Notice

Slidegeist is provided for educational and research purposes only. Users must ensure they have the legal right to access, download, or process any video files they use with this tool. The author does not endorse or facilitate copyright infringement or violation of platform terms of service.

License

MIT License - Copyright (c) 2025 Christopher Albert

See LICENSE for details.

Contributing

Contributions welcome! Please see CONTRIBUTING.md for guidelines.