FFmpeg Kit macOS Code Signing Crash

Problem

Flutter macOS app builds successfully but crashes immediately at launch with a library loading failure. The crash is caused by FFmpeg Kit's Full GPL variant having runtime dependencies on homebrew-installed libraries (like fontconfig) that fail macOS code signature validation.

Context / Trigger Conditions

• Platform: macOS only (iOS and Android are not affected)
• Package: Using ffmpeg_kit_flutter_new (Full GPL variant)
• Symptom: App builds successfully but crashes on launch
• Crash log shows:

  Library not loaded: /opt/homebrew/*/libfontconfig.1.dylib
  Referenced from: .../libswresample.framework/...
  Reason: code signature in (.../libfontconfig.1.dylib) not valid for use in process:
  mapping process and mapped file (non-platform) have different Team IDs
  

Root Cause

The ffmpeg_kit_flutter_new package is the "Full GPL" variant which includes many FFmpeg libraries for advanced features like text rendering (drawtext filter). These libraries have external dependencies on system fonts via libfontconfig.

On macOS, when the app tries to load libswresample.framework, it attempts to also load libfontconfig.1.dylib from homebrew. macOS code signing validation rejects this because the homebrew library has a different Team ID than your app.

Solution

Switch from ffmpeg_kit_flutter_new (Full GPL) to ffmpeg_kit_flutter_new_min (Minimal).

Step 1: Update pubspec.yaml

# Before
ffmpeg_kit_flutter_new: ^3.2.0

# After
ffmpeg_kit_flutter_new_min: ^3.1.0

Step 2: Update imports in all Dart files

// Before
import 'package:ffmpeg_kit_flutter_new/ffmpeg_kit.dart';
import 'package:ffmpeg_kit_flutter_new/ffprobe_kit.dart';
import 'package:ffmpeg_kit_flutter_new/return_code.dart';

// After
import 'package:ffmpeg_kit_flutter_new_min/ffmpeg_kit.dart';
import 'package:ffmpeg_kit_flutter_new_min/ffprobe_kit.dart';
import 'package:ffmpeg_kit_flutter_new_min/return_code.dart';

Step 3: Clean and rebuild

flutter clean
rm -f macos/Podfile.lock
flutter pub get
flutter run -d macos

What Features Are Preserved

The minimal variant includes everything needed for typical video apps:

• h264/libx264 video encoding
• AAC audio encoding
• VideoToolbox hardware acceleration (Apple platforms)
• Standard filters: overlay, crop, scale, concat, amix
• FFprobe for media information

What Features Are Removed

The minimal variant does NOT include:

• drawtext filter (font rendering) - use PNG overlays instead
• Advanced codec libraries with external dependencies
• Features requiring fontconfig, freetype, etc.

Verification

After the fix:

1. flutter run -d macos should launch the app without crashing
2. Video encoding/decoding operations should work normally
3. iOS builds continue to work (they weren't affected)

Example

Find files needing import updates:

grep -r "ffmpeg_kit_flutter_new" lib/ --include="*.dart" -l

Update all imports (sed example):

find lib -name "*.dart" -exec sed -i '' \
  's/ffmpeg_kit_flutter_new/ffmpeg_kit_flutter_new_min/g' {} \;

Notes

• This issue only affects macOS; iOS and Android don't have the same code signing restrictions
• The error message is misleading - it mentions fontconfig but the fix is changing FFmpeg Kit variants
• If you actually need drawtext filter on macOS, you'd need to bundle fontconfig with proper signing (complex)
• Alternative: Use the official ffmpeg_kit_flutter from arthenica if you need more control over variants

References

• ffmpeg_kit_flutter_new on pub.dev
• ffmpeg_kit_flutter_new_min on pub.dev
• Apple Code Signing Documentation