videobeaux/docs/programs/effects/stack_2x.md

stack_2x

Description

Stacks two videos vertically (one on top of the other) while preserving the original orientation and aspect ratio of each source.
This module creates a clean two-layer composite, useful for comparison videos, collage work, diptychs, and multi-view layouts.

Purpose

stack_2x is designed for creators who want:

• a simple vertical two-video layout,
• a clean and deterministic stacking tool with minimal configuration,
• a fast way to create split-screen or comparison visuals,
• diptych or layered collage structures,
• multi-camera or multi-source presentations.

How It Works

1. Load Primary Input
   The global input (-i input.mp4) forms the top (or first) layer.
2. Load Secondary Input
   The --input2 path loads the second video, which becomes the bottom layer.
3. Vertical Stacking
   The two frames are aligned vertically using FFmpeg’s stacking filters.
   No rotation, flipping, or aspect correction is applied unless done elsewhere in the chain.
4. Encoding
   The resulting double-height composite is encoded using the global Videobeaux settings (CRF, codec, pixel format).

Program Template

videobeaux -P stack_2x \
  -i input.mp4 \
  -o output.mp4 \
  --input2 VALUE

Arguments

• input2 — Path to the second video file to place beneath the primary input.

Real World Example

videobeaux -P stack_2x \
  -i myvideo.mp4 \
  -o stack_2x_styled.mp4 \
  --input2 EXAMPLE

Program Output

Technical Notes

• Both videos should ideally share the same width; otherwise, FFmpeg will auto-scale or pad depending on filter rules.
• Stacked output height = sum of both video heights.
• Audio is typically taken from the primary input unless modified elsewhere in the pipeline.
• Works well in workflows where temporal sync matters (side-by-side camera takes, A/B comparison, performance studies).
• For mismatched aspect ratios, consider preprocessing via convert_dims or resize.

Recommended Usage

• A/B comparison videos.
• Performance or rehearsal footage with two simultaneous takes.
• Collage art that arranges multiple perspectives vertically.
• Multi-layer stacks inside Lagkage.
• Vertical diptych compositions for experimental film or social formats.

Quality Tips

• The cleaner the scaling match between the two videos, the sharper the final composite.
• Use lower CRF for crisp splits with sharp geometry.
• To harmonize color or lighting between the two clips, apply grading (lut_apply, gamma_fix) before stacking.
• Combine with stack_3x or other stacking modules for multi-row layouts.
• Use resize to unify widths before stacking for the most predictable results.