Generate thumbnail for Flutter web video files

I'm making a video player, for which I am selecting a video and trying to generate a thumbnail to show.

I'm using the following code to pick Images/videos from the file picker.

import 'dart:html' as html;

startWebFilePicker() async {
  html.InputElement uploadInput = html.FileUploadInputElement();
  uploadInput.multiple = true;
  uploadInput.draggable = true;
  uploadInput.click();

  uploadInput.onChange.listen((e) {
    final files = uploadInput.files;
    final file = files[0];
    entryFile = file;
    String mimeType = lookupMimeType(file.name);

    mime = mimeType.split('/')[0];

    fileType = mimeType.split('/')[1];
    baseName = file.name;
    final reader = new html.FileReader();

    reader.onLoadEnd.listen((e) {
      _handleResult(reader.result);
    });
    reader.readAsDataUrl(file);
  });
}
  

How can I generate a thumbnail using the video file picked?