Flutter: Can we save a Canvas/CustomPainter to a gif or continuous pictures or event a video?

Question

Can we export custom painter used animation controller to a gif image or continuous images or event a video such as mp4 file?

Answer 1

Yes I did it one time (2 years ago) and I converted a Flutter Animation to a mp4 file. unfortunately I couldn't find the code. please follow the steps to make what you want.

1. capture your widget with RenderRepaintBoundary like below code https://api.flutter.dev/flutter/rendering/RenderRepaintBoundary/toImage.html

    class PngHome extends StatefulWidget {
      const PngHome({super.key});
   
      @override
      State<PngHome> createState() => _PngHomeState();
    }
   
    class _PngHomeState extends State<PngHome> {
      GlobalKey globalKey = GlobalKey();
   
      Future<void> _capturePng() async {
        final RenderRepaintBoundary boundary = globalKey.currentContext!.findRenderObject()! as RenderRepaintBoundary;
        final ui.Image image = await boundary.toImage();
        final ByteData? byteData = await image.toByteData(format: ui.ImageByteFormat.png);
        final Uint8List pngBytes = byteData!.buffer.asUint8List();
        print(pngBytes);
      }
   
      @override
      Widget build(BuildContext context) {
        return RepaintBoundary(
          key: globalKey,
          child: Center(
            child: TextButton(
              onPressed: _capturePng,
              child: const Text('Hello World', textDirection: TextDirection.ltr),
            ),
          ),
        );
      }
   
    }
   

2. save each image like this

   import 'package:path_provider/path_provider.dart';
   import 'dart:io';
   
   Uint8List imageInUnit8List = // store unit8List image here ;
   final tempDir = await getTemporaryDirectory();
   File file = await File('${tempDir.path}/image.png').create();
   file.writeAsBytesSync(imageInUnit8List);
   

---

3. you need to capture each frame of your Animation and save it to a directory. with special naming for example (1.png,2.png .... 1000.png)

    @override
    Widget build(BuildContext context) {
    return AnimatedBuilder(
      animation: _controller,
      child: theChildWidet() // important use child for performance 
      builder: (BuildContext context, Widget? child) {
   
        CaptureScreenAndSave(_controller.value) /// <- capture each frame
   
        return Transform.rotate(
          angle: _controller.value * 2.0 * math.pi,
          child: child,
        );
      },
    );
    }
   

4. install ffmpeg https://pub.dev/packages/ffmpeg_kit_flutter and use it to execute FFMPEG command

   import 'package:ffmpeg_kit_flutter/ffmpeg_kit.dart';
   
   FFmpegKit.execute('your command').then((session) async {
   final returnCode = await session.getReturnCode();
   
   if (ReturnCode.isSuccess(returnCode)) {
   
    // SUCCESS
   
   } else if (ReturnCode.isCancel(returnCode)) {
   
    // CANCEL
   
   } else {
   
    // ERROR
   
   }
   });
   

5. search for a command to convert your images with ffmpeg to Gif Or Mp4 (some thing like these Example1 or Example2)