lottie_fixup 0.1.0

Fixes Lottie/Bodymovin exports that crash or freeze the lottie Flutter package: audio layers, empty precomps, and loopOut()/loopIn() expressions.

lottie_fixup

Fixes Lottie/Bodymovin exports that crash or freeze the lottie Flutter package: audio layers, empty precomps, and loopOut() / loopIn() expressions.

Features

• Stops the audio-layer crash — After Effects audio layers ("ty": 6) ship without the transform block lottie expects, which throws Null check operator used on a null value. This package strips them.
• Bakes loopOut() / loopIn() expressions into real keyframes, so looping animations don't freeze after their first cycle (lottie doesn't execute expressions).
• Prunes empty precomps and now-unreferenced assets left behind by the fixes above.
• Use it at load time (drop-in decoder, no build step) or ahead of time (CLI, zero runtime cost).

Getting started

Add the dependency:

dependencies:
  lottie_fixup: ^0.1.0

Usage

At load time — no build step

Drop fixupLottieDecoder into any lottie loading API that takes a decoder:

import 'package:lottie/lottie.dart';
import 'package:lottie_fixup/lottie_fixup.dart';

Lottie.asset('assets/character.json', decoder: fixupLottieDecoder)

Safe to apply unconditionally, even to files already fixed ahead of time — fix is a no-op when there's nothing left to do. This adds a JSON decode/walk/re-encode once per composition load, not per frame. For larger files, pass backgroundLoading: true to move that work off the UI isolate:

Lottie.asset(
  'assets/character.json',
  decoder: fixupLottieDecoder,
  backgroundLoading: true,
)

Ahead of time — CLI

For an animation that ships in every build and never changes, fix it once and skip the runtime cost entirely:

dart pub global activate lottie_fixup
lottie_fixup diagnose assets/animations/*.json   # report only, no changes
lottie_fixup fix assets/animations/*.json        # fix in place

Library

import 'dart:convert';
import 'dart:io';
import 'package:lottie_fixup/lottie_fixup.dart';

final file = File('animation.json');
final doc = jsonDecode(file.readAsStringSync()) as Map<String, dynamic>;

final result = fix(doc); // mutates doc in place
if (result.changed) {
  file.writeAsStringSync(jsonEncode(doc));
}

What this does not fix

• Expressions other than loopOut/loopIn (e.g. wiggle, valueAtTime) are reported (diagnose, or FixResult.bake.skippedExpressions) but left untouched.
• A layer missing ks for a reason other than being an audio layer is flagged (SanitizeResult.layersMissingTransform) rather than silently removed, since that could be a real authoring mistake worth checking by hand.

Additional information

If this package saved you a debugging session, consider buying me a coffee.