The library that is responsible for different scheduling is flutter/scheduler. This also includes animations. To use the library, simply import package:flutter/scheduler.dart – in this case, timeDilation is all that you need.

Now you can set the variable timeDilation to a custom double. The value 1.0 is the default animation speed. Setting it to 2.0 will slow down all animations by a factor of two.

import 'package:flutter/scheduler.dart' show timeDilation;

// ...

timeDilation = 2.0; // Slow down animations by factor two

As timeDilation is a global variable, you can set it anywhere in the code, e.g. in main():

import 'package:flutter/scheduler.dart' show timeDilation;

void main() {
  timeDilation = 3.0;
  runApp(new MyApp());
}

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