9b724f33e3
## New Skill: video-comparer v1.0.0 - Compare original and compressed videos with interactive HTML reports - Calculate quality metrics (PSNR, SSIM) for compression analysis - Generate frame-by-frame visual comparisons (slider, side-by-side, grid) - Extract video metadata (codec, resolution, bitrate, duration) - Multi-platform FFmpeg support with security features ## transcript-fixer Enhancements - Add async AI processor for parallel processing - Add connection pool management for database operations - Add concurrency manager and rate limiter - Add audit log retention and database migrations - Add health check and metrics monitoring - Add comprehensive test suite (8 new test files) - Enhance security with domain and path validators ## Marketplace Updates - Update marketplace version from 1.8.0 to 1.9.0 - Update skills count from 15 to 16 - Update documentation (README.md, CLAUDE.md, CHANGELOG.md) 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>
97 lines
3.4 KiB
Markdown
97 lines
3.4 KiB
Markdown
# Video Quality Metrics Reference
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## Contents
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- [PSNR (Peak Signal-to-Noise Ratio)](#psnr-peak-signal-to-noise-ratio) - Pixel-level similarity measurement
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- [SSIM (Structural Similarity Index)](#ssim-structural-similarity-index) - Perceptual quality measurement
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- [VMAF (Video Multimethod Assessment Fusion)](#vmaf-video-multimethod-assessment-fusion) - Machine learning-based quality prediction
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- [File Size and Bitrate Considerations](#file-size-and-bitrate-considerations) - Compression targets and guidelines
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## PSNR (Peak Signal-to-Noise Ratio)
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### Definition
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PSNR measures the ratio between the maximum possible power of a signal and the power of corrupting noise. It's commonly used to measure the quality of reconstruction of lossy compression codecs.
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### Scale
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- **Range**: Typically 20-50 dB
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- **Higher is better**: More signal, less noise
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### Quality Interpretation
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| PSNR (dB) | Quality Level | Use Case |
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|-----------|---------------|----------|
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| < 20 | Poor | Unacceptable for most applications |
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| 20-25 | Low | Acceptable for very low-bandwidth scenarios |
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| 25-30 | Fair | Basic video streaming |
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| 30-35 | Good | Standard streaming quality |
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| 35-40 | Very Good | High-quality streaming |
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| 40+ | Excellent | Near-lossless quality, archival |
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### Calculation Formula
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```
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PSNR = 10 * log10(MAX_I^2 / MSE)
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```
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Where:
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- MAX_I = maximum pixel value (255 for 8-bit images)
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- MSE = mean squared error
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## SSIM (Structural Similarity Index)
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### Definition
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SSIM is a perceptual metric that quantifies image quality degradation based on structural information changes rather than pixel-level differences.
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### Scale
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- **Range**: 0.0 to 1.0
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- **Higher is better**: More structural similarity
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### Quality Interpretation
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| SSIM | Quality Level | Use Case |
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|------|---------------|----------|
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| < 0.70 | Poor | Visible artifacts, structural damage |
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| 0.70-0.80 | Fair | Noticeable quality loss |
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| 0.80-0.90 | Good | Acceptable for most streaming |
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| 0.90-0.95 | Very Good | High-quality streaming |
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| 0.95-0.98 | Excellent | Near-identical perception |
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| 0.98+ | Perfect | Indistinguishable from original |
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### Components
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SSIM combines three comparisons:
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1. **Luminance**: Local brightness comparisons
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2. **Contrast**: Local contrast comparisons
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3. **Structure**: Local structure correlations
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## VMAF (Video Multimethod Assessment Fusion)
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### Definition
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VMAF is a machine learning-based metric that predicts subjective video quality by combining multiple quality metrics.
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### Scale
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- **Range**: 0-100
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- **Higher is better**: Better perceived quality
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### Quality Interpretation
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| VMAF | Quality Level | Use Case |
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|-------|---------------|----------|
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| < 20 | Poor | Unacceptable |
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| 20-40 | Low | Basic streaming |
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| 40-60 | Fair | Standard streaming |
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| 60-80 | Good | High-quality streaming |
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| 80-90 | Very Good | Premium streaming |
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| 90+ | Excellent | Reference quality |
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## File Size and Bitrate Considerations
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### Compression Targets by Use Case
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| Use Case | Size Reduction | PSNR Target | SSIM Target |
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|----------|----------------|-------------|-------------|
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| Social Media | 40-60% | 35-40 dB | 0.95-0.98 |
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| Streaming | 50-70% | 30-35 dB | 0.90-0.95 |
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| Archival | 20-40% | 40+ dB | 0.98+ |
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| Mobile | 60-80% | 25-30 dB | 0.85-0.90 |
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### Bitrate Guidelines
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| Resolution | Target Bitrate (1080p equivalent) |
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|------------|-----------------------------------|
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| 480p | 1-2 Mbps |
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| 720p | 2-5 Mbps |
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| 1080p | 5-10 Mbps |
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| 4K | 20-50 Mbps | |