Fixing Interlace Artifacts with VirtualDub: Step-by-Step Deinterlace GuideInterlacing artifacts—comb-like edges, flicker, and motion ghosting—remain common when dealing with older video sources such as VHS captures, TV recordings, or some broadcast rips. VirtualDub is a lightweight, free Windows video processing tool favored by hobbyists and professionals for frame-level editing, filtering, and batch processing. This guide walks you through identifying interlace problems, choosing the right deinterlace filter, configuring settings, and producing clean progressive output.
What is interlacing and why it causes artifacts
Interlacing was designed to reduce bandwidth by splitting each video frame into two fields captured at slightly different times (odd and even lines). When displayed on progressive screens or when motion is present, the temporal difference between fields appears as:
- combing (diagonal or serrated edges on moving objects),
- line twitter or flicker (fine horizontal detail shimmering),
- loss of vertical resolution when fields are blended improperly.
Effective deinterlacing restores a smooth progressive image without losing detail or introducing blurring, judder, or combing.
How to identify interlace artifacts
Look for:
- Diagonal comb-like serrations along moving edges.
- Horizontal line flicker on high-frequency textures (hair, grass).
- Uneven motion where alternate scanlines jump.
To confirm, step through the video one frame at a time in VirtualDub. If adjacent fields show different object positions, it’s interlaced.
Preparing VirtualDub
- Download VirtualDub (and VirtualDub FilterPack if needed). Use the 32-bit build if you plan to run 32-bit filters; 64-bit builds exist but some older filters require 32-bit VirtualDub.
- Place any external filters (.vdf/.vcf or .vf files) into VirtualDub’s plugins folder if required.
- Open your video: File → Open video file.
Recommended deinterlace filters for VirtualDub
- Decomb (e.g., Deshaker’s Decomb or Avisynth-style Decomb ports): adaptive, preserves detail when frames are already progressive.
- Yadif (ported to VirtualDub or via Avisynth): simple and good quality for motion.
- FieldDeinterlace (basic, fast — may reduce vertical resolution).
- QTGMC (via Avisynth — highest quality but requires Avisynth, scripting, and longer processing time).
If you want the best balance between quality and simplicity inside VirtualDub, start with an adaptive decomb filter or Yadif port.
Step-by-step: Basic deinterlacing in VirtualDub (adaptive decomb)
- Open your file (File → Open video file).
- Set video mode: Video → Full processing mode.
- Add filter: Video → Filters → Add.
- Choose your deinterlace filter (e.g., “Decomb” or “Yadif” if available) and click OK.
- Configure filter settings:
- Mode: Adaptive or Deinterlace detected frames only (helps avoid blurring progressive content).
- Thresholds: Keep default initially; lower values make the filter more sensitive (may deinterlace more frames), higher values reduce false positives.
- Motion detection: Enable if available to preserve static areas.
- Preview: Use the preview window and step through frames to check for remaining combing or excessive blur.
- If artifacts remain, adjust sensitivity or try a different deinterlace algorithm (switch between bob, weave, blend, or motion-compensated options if offered).
- When satisfied, set compression: Video → Compression → choose your codec and configure quality.
- Save output: File → Save as AVI. (For other formats, use VirtualDub’s export options or re-wrap with external tools.)
Advanced workflow: Using Avisynth + QTGMC for best quality
For high-quality results, combine VirtualDub with Avisynth and QTGMC (motion-compensated, detail-preserving). This requires more setup but yields superior deinterlacing.
- Install Avisynth+ (recommended) and VirtualDub.
- Install QTGMC and dependencies (MVTools, FFT3DFilter, etc.).
- Create an Avisynth script (.avs) that loads your source and applies QTGMC, for example:
DirectShowSource("input.avi") QTGMC(Preset="Slow", Kernel=2, TR=2) - Open the .avs script in VirtualDub (File → Open video file).
- Preview, then save using your chosen compression.
QTGMC has many parameters (Preset, TR, Sharpness) — use Preset=“Slow” or “Slower” for best quality; “Fast” or “Medium” for speed.
Tips to preserve quality
- Always prefer full processing mode to allow filter effects.
- Use adaptive filters to avoid deinterlacing already progressive frames.
- Compare output at 100% zoom and step through frames; small preview windows can hide combing.
- Keep a lossless intermediate (like Lagarith or HuffYUV) if you’ll re-edit; final encode should use your delivery codec.
- If audio must remain synchronized, use VirtualDub’s audio settings or process audio separately and remux.
Troubleshooting common issues
- Excessive blurring: Lower deinterlace aggressiveness or use a higher-quality filter (QTGMC).
- Remaining combing: Increase sensitivity or enable motion detection; try motion-compensated filters.
- Flicker on fine detail: Try temporal smoothing options or trade off some sharpness for stability.
- Filters not visible/working: Ensure plugin is compatible with your VirtualDub build (32-bit vs 64-bit).
Batch deinterlacing
VirtualDub supports command-line processing and jobs for batch work:
- Use File → Save as AVI with multiple files queued, or create a script using VirtualDub’s command-line options to process folders of files with the same filter chain.
Example settings to try (starting points)
- Decomb (adaptive): Mode = Detect & Deinterlace; Threshold = default; Motion detection = On.
- Yadif (single-field): Mode = Bob for smooth motion; combine with a mild sharpening filter if detail is soft.
- QTGMC (Avisynth): Preset = Medium or Slow; TR = 2; Sharpness = 0.5–1.0.
Final export considerations
- Use a lossless intermediate if you plan further edits.
- For final viewing, encode with a modern codec (H.264/H.265) using a two-pass or CRF workflow; keep bitrate sufficient to preserve deinterlaced detail.
- Check final file on the target display to ensure motion appears natural.
If you want, I can:
- Provide an Avisynth QTGMC script tuned to a specific sample (interlaced VHS vs. broadcast),
- Recommend exact VirtualDub filters (with download locations) compatible with 64-bit or 32-bit builds,
- Or generate a sample batch command to process a folder of AVIs.
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