Create karaoke effect Flutter

you can use animated_text_kit package

https://pub.dev/packages/animated_text_kit

Use a Stack to put a layer of red Text on top of a layer of white Text. And then use ClipRect to slowly show the top layer.

Basically:

Stack
[
  - ClipRect
    - Red Text
  - White Text
]

The most difficulty part is "time sync", i.e. to know the speed of the flow, because in a song, some words are gonna be much faster than other words. Tell us your plan of time sync, and I can further suggest which type of animation controller is best for this task.