更新：自从我的原始答案以来，还有另一个具有友好API的软件包https://pub.dev/packages/flutter_video_compress

https://pub.dartlang.org/packages/flutter_ffmpeg非常好，并且有详尽的说明

import 'package:flutter_ffmpeg/flutter_ffmpeg.dart';

 final FlutterFFmpeg _flutterFFmpeg = new FlutterFFmpeg();

 _flutterFFmpeg.execute("-i file1.mp4 -c:v mpeg4 file2.mp4").then((rc) => print("FFmpeg process exited with rc $rc"));

检查rc代码，如果成功，请打开file2.mp4，它是压缩/处理后的文件。