source-compare

name	source-compare
description	This skill should be used when the user asks "compare these videos", "which source is better", "compare blu-ray vs web", "which release should I use", "compare video quality", or needs to evaluate multiple versions of the same content to determine which has better quality.

Video Source Comparison

Compare multiple video sources to determine which has better quality. Higher bitrate or resolution does not automatically mean better quality.

Core Principle

Quality = how closely video resembles original master.

When comparing sources:

• Both derive from some common master
• The better source is closer to that master
• Technical specs (bitrate, resolution) are secondary to actual visual quality

Comparison Workflow

Step 1: Gather Metadata

Run MediaInfo on both sources:

mediainfo source_a.mkv > source_a_info.txt
mediainfo source_b.mkv > source_b_info.txt

Compare:

• Resolution
• Bitrate
• Encoder used
• Color space parameters
• HDR metadata (if applicable)

Note: Higher numbers don't guarantee better quality.

Step 2: Extract Comparison Frames

Choose frames that reveal quality differences:

Good comparison frames:

• Dark scenes with gradients (reveals banding)
• Scenes with fine texture (hair, fabric, foliage)
• High motion scenes (reveals compression)
• Scenes with text or sharp edges (reveals filtering)
• Areas with strong colors (reveals color handling)

Extract frames with ffmpeg:

# Extract frame at specific timestamp
ffmpeg -ss 00:15:30 -i source.mkv -frames:v 1 frame_15m30s.png

# Extract multiple frames
ffmpeg -ss 00:10:00 -i source.mkv -frames:v 1 frame1.png
ffmpeg -ss 00:25:00 -i source.mkv -frames:v 1 frame2.png
ffmpeg -ss 00:45:00 -i source.mkv -frames:v 1 frame3.png

Step 3: Visual Comparison

Using SlowPics (https://slow.pics):

1. Upload comparison frames from each source
2. Uncheck "Show border" and "Smooth scaling"
3. Use clicker mode (not slider)
4. Press number keys (1/2/3) to switch rapidly between sources

What to look for:

Area	Better Source Shows
Dark gradients	Smoother transitions, less banding
Edges	Clean edges, no haloing/ringing
Textures	Preserved grain/detail, not smeared
Colors	Natural, not oversaturated or shifted
Compression	Less blocking, less mosquito noise

Step 4: Check for Filtering

Signs of harmful filtering:

Lowpassing (blur):

• Soft, smeared appearance
• Fine details less defined than other source
• Some Blu-ray authoring studios apply this

Sharpening:

• Haloing around edges (bright/dark outlines)
• Unnatural crispness
• Line warping on straight edges

Color manipulation:

• Oversaturated colors
• Crushed blacks or blown highlights
• Different color grading than other source

Upscaling:

• Details too sharp for claimed resolution
• AI hallucinations (invented details)
• Native resolution lower than file resolution

Common Scenarios

Blu-ray vs Web

Blu-ray usually better when:

• Same master, Blu-ray has more bitrate
• No filtering applied during authoring
• Proper color space handling

Web can be better when:

• Blu-ray has lowpass filter applied
• Web has newer/better master
• Blu-ray is poor upscale from SD source
• Web version has better color grading

Multiple Blu-ray Releases

Different authoring studios, regions, or editions can have different quality:

• Check authoring studio (some are known for lowpassing)
• Compare frame-by-frame for filtering
• Look for remastered vs original master

SD vs HD

HD version better when:

• Truly native HD content
• Good upscale from clean SD master

SD version better when:

• HD is poorly upscaled from SD source
• HD has additional filtering damage
• SD is closer to original DVD master

Red Flags

Higher bitrate source might be worse if:

• Encoded with inferior encoder (NVENC vs x264)
• Has filtering applied (sharpening, lowpass)
• Is upscaled from lower resolution
• Has wrong color space applied

Higher resolution source might be worse if:

• Upscaled from lower resolution original
• Has AI upscaling artifacts
• Native production resolution was lower

Quick Decision Guide

Comparison	Check First	Likely Winner
Blu-ray vs Web	Filtering, authoring	Depends on studio
4K vs 1080p	Native resolution	If native, 4K
HEVC vs AVC	Encoder, settings	Neither inherently
High vs low bitrate	Encoder efficiency	Higher if same encoder
HDR vs SDR	HDR legitimacy	SDR if HDR is fake

Tools Reference

• SlowPics (slow.pics) - Frame comparison hosting
• vs-preview - VapourSynth comparison tool
• mpv - Frame extraction, playback comparison
• MediaInfo - Metadata comparison

Additional Resources

• JET Guide: https://jaded-encoding-thaumaturgy.github.io/JET-guide/
• ${CLAUDE_PLUGIN_ROOT}/references/quality-myths.md - Why specs don't equal quality
• ${CLAUDE_PLUGIN_ROOT}/references/artifacts.md - What quality issues look like