Swift Package Demo Recording

Overview

Record and optimize demo GIFs for Swift package READMEs. Swift packages need a separate demo app since SwiftUI previews only run in Xcode Canvas, not the iOS Simulator.

When to Use

• Adding demo GIFs to a Swift package README
• Recording iOS Simulator for documentation
• User asks to "record a demo" or "add GIFs to README"

Critical Understanding

digraph demo_flow {
    "SwiftUI Preview" [shape=box];
    "iOS Simulator" [shape=box];
    "Xcode Canvas only" [shape=box, style=filled, fillcolor=lightyellow];
    "Recordable with xcrun" [shape=box, style=filled, fillcolor=lightgreen];

    "SwiftUI Preview" -> "Xcode Canvas only" [label="runs in"];
    "Demo App" -> "iOS Simulator" [label="runs in"];
    "iOS Simulator" -> "Recordable with xcrun";
}

SwiftUI #Preview macros CANNOT be recorded. You must create a demo app.

Quick Reference

Step	Command/Action
Create demo dir	mkdir -p demo
Boot simulator	xcrun simctl boot "iPhone SE (3rd generation)"
Open simulator	open -a Simulator
Record video	xcrun simctl io booted recordVideo --codec=h264 demo/raw.mov
Stop recording	Ctrl+C
Convert to GIF	See FFmpeg command below
Optimize GIF	gifsicle -O3 --lossy=80 demo/out.gif -o demo/out.gif

Demo App Setup

Create demo/DemoApp/ with Xcode project that imports your package locally:

1. In Xcode: File → New → Project → iOS App
2. Save in demo/DemoApp/
3. File → Add Package Dependencies → Add Local → select package root
4. Import and use your library in the app

Critical: Use local package reference, not remote URL, to test current development code.

Recording Commands

# Boot simulator (smaller = smaller GIF)
xcrun simctl boot "iPhone SE (3rd generation)"
open -a Simulator

# Run demo app in Xcode (Cmd+R), then record
xcrun simctl io booted recordVideo --codec=h264 demo/raw.mov
# Ctrl+C to stop

GIF Conversion

REQUIRED: Before converting .mov files to GIF, you MUST ask the user using AskUserQuestion:

Question: "How should the GIF be sized?"
Options:
- Full size (keep entire screen including status bar)
- Cropped (remove status bar and bottom navigation)

Do NOT assume cropping. Do NOT convert without asking first.

Full Size (default)

ffmpeg -i demo/raw.mov -filter_complex \
  "[0:v] fps=12,scale=300:-1:flags=lanczos,split [a][b]; \
   [a] palettegen=max_colors=128:stats_mode=diff [p]; \
   [b][p] paletteuse=dither=floyd_steinberg:diff_mode=rectangle" \
  -y demo/output.gif

gifsicle -O3 --lossy=80 demo/output.gif -o demo/output.gif

Cropped (removes status bar and bottom nav)

ffmpeg -i demo/raw.mov -filter_complex \
  "[0:v] crop=in_w:in_h*0.55:0:in_h*0.12,fps=12,scale=300:-1:flags=lanczos,split [a][b]; \
   [a] palettegen=max_colors=128:stats_mode=diff [p]; \
   [b][p] paletteuse=dither=floyd_steinberg:diff_mode=rectangle" \
  -y demo/output.gif

gifsicle -O3 --lossy=80 demo/output.gif -o demo/output.gif

Crop parameters: crop=in_w:in_h*0.55:0:in_h*0.12 keeps 55% height starting at 12% from top.

README Integration

<p align="center">
  <img src="demo/demo1.gif" width="280" alt="Demo 1">&nbsp;&nbsp;<img src="demo/demo2.gif" width="280" alt="Demo 2">
</p>

Side-by-side: Use    between images, width 240-280px each.

.gitignore

# Demo - ignore everything except GIFs
demo/*
!demo/*.gif

Common Mistakes

Mistake	Fix
Converting without asking about sizing	Always ask user: full size or cropped?
Trying to record SwiftUI previews	Create demo app, run in simulator
"No devices booted" error	Run xcrun simctl boot "iPhone SE (3rd generation)" first
Demo app uses remote package	Use Add Local package reference
API mismatch after package changes	Xcode → File → Packages → Reset Package Caches
GIFs too large (>1MB)	Reduce fps (12), scale (300px), use gifsicle
Recording before app runs	Run app in Xcode (Cmd+R) first, THEN start recording

Target Sizes

Type	Width	FPS	Target Size
Hero demo	280-300px	12	< 200KB
Feature demo	240px	10-12	< 150KB