| 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:
ffmpeg -ss 00:15:30 -i source.mkv -frames:v 1 frame_15m30s.png
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):
- Upload comparison frames from each source
- Uncheck "Show border" and "Smooth scaling"
- Use clicker mode (not slider)
- 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
