robbyt/telecine-detect

Telecine and Interlacing Detection

Detect whether video content is telecined (reversible) or truly interlaced (not reversible), and advise on proper handling. Getting this wrong destroys video quality.

Critical Distinction

Telecine (3:2 Pulldown):

• 24fps film content converted to 30fps for NTSC broadcast
• Creates repeating pattern of combing across frames
• Can be reversed nearly losslessly via IVTC (inverse telecine)
• Original 24fps frames can be recovered

True Interlacing:

• Content actually captured at 60 interlaced fields per second
• Each field is unique temporal information
• Cannot be reversed without quality loss
• Deinterlacing merges or discards fields

The Common Mistake

Seeing combing → Immediately running a deinterlacer

Why this is wrong for telecined content:

• Deinterlacers throw away half the vertical resolution
• They cannot distinguish telecine from true interlacing
• The original 24 progressive frames are lost
• Result is a blurry, lower-quality video

Correct approach:

1. First detect if content is telecined or truly interlaced
2. If telecined → use IVTC to recover original frames
3. If truly interlaced → only then consider deinterlacing

Detection Workflow

Step 1: Check MediaInfo

Look for these fields:

Scan type: Interlaced or Progressive
Scan order: Top Field First (TFF) or Bottom Field First (BFF)

Note: MediaInfo only shows container/stream flags. Content can be flagged as interlaced but actually be telecined, or flagged progressive but have telecine applied.

Step 2: Visual Inspection

Open in mpv and step through frames (. and , keys):

Telecine indicators:

• Combing appears on some frames but not others
• Pattern repeats (e.g., every 5th frame has combing)
• Combing only on specific parts of frame where motion occurred
• 3:2 pattern: 2 clean frames, then 3 frames with combing alternating

True interlacing indicators:

• Every frame shows combing on all motion
• No repeating pattern
• Combing appears uniformly across frame

Step 3: Confirm with Frame Analysis

For telecine, look for the 3:2 pulldown pattern:

Frame 1: Progressive (A)
Frame 2: Progressive (A)
Frame 3: Interlaced (A top + B bottom)
Frame 4: Interlaced (B top + C bottom)
Frame 5: Progressive (C)
... pattern repeats

Count frames between clean (progressive) frames. If pattern is consistent (typically 2-3-2-3 or similar), it's telecine.

Handling Telecined Content

Tools for IVTC

Wobbly (Recommended):

• GUI tool for manual telecine pattern matching
• Handles irregular patterns and scene changes
• Guide: https://wobbly.encode.moe

VapourSynth VIVTC:

• Automated IVTC for consistent patterns
• Part of VapourSynth toolchain

avisynth/vapoursynth TFM+TDecimate:

• Classic IVTC combination
• TFM matches fields, TDecimate removes duplicates

IVTC Process

1. Identify the telecine cadence (pattern)
2. Match fields to reconstruct original frames
3. Decimate (remove) duplicate frames
4. Result: Original 24fps progressive content

Handling True Interlacing

Only when content is confirmed truly interlaced:

Deinterlacing options (quality varies):

• QTGMC (VapourSynth/Avisynth) - highest quality, slow
• yadif - fast, moderate quality
• bwdif - improved yadif

Doubling options (60fps output):

• Bob deinterlacing - fast, doubles frame rate
• QTGMC bob - higher quality bob

Quick Reference

| Symptom | Likely Cause | Action | |---------|--------------|--------| | Combing on some frames only | Telecine | Use IVTC | | Repeating pattern of combing | Telecine | Use IVTC | | Every frame has combing | True interlacing | Deinterlace | | DVD/NTSC source, 29.97fps | Often telecine | Check pattern | | Sports/news content | Often true interlacing | Deinterlace | | Film/movie content | Often telecine | Use IVTC |

Red Flags

Don't deinterlace if:

• Source is a movie or scripted TV show (likely telecine)
• Combing appears in a pattern
• MediaInfo shows 23.976fps original rate
• Source is from DVD/Blu-ray of film content

Consider deinterlacing if:

• Live broadcast content (sports, news)
• Home video footage
• Every single frame shows combing
• No discernible pattern

Additional Resources

• fieldbased.media - Comprehensive interlacing guide
• https://wobbly.encode.moe - Wobbly IVTC guide
• ${CLAUDE_PLUGIN_ROOT}/references/telecine.md - Detailed telecine patterns