flutter_macos_video_player Can't load video from assets

I'm trying to use this video player in a presentation app, similar to Powerpoint or Keynote.

I have videos packaged with my app assets that I'd like to play in the presentation. However, VideoPlayerController.asset("...") triggers an unimplemented error when initialize()ing.

Code:

_videoPlayerController = VideoPlayerController.asset("assets/content/demo_graph-paper.mov");
await _videoPlayerController.initialize();
_videoPlayerController.play();

Error:

[ERROR:flutter/lib/ui/ui_dart_state.cc(198)] Unhandled Exception: PlatformException(video_player, not implemented, null, null)
#0      VideoPlayerApi.create (package:video_player_platform_interface/messages.dart:189:7)
<asynchronous suspension>
#1      MethodChannelVideoPlayer.create (package:video_player_platform_interface/method_channel_video_player.dart:53:37)
<asynchronous suspension>
#2      VideoPlayerController.initialize (package:video_player/video_player.dart:363:19)
<asynchronous suspension>
#3      _PresentationState._setupVideoPlayer (package:presentations/main.dart:88:5)
<asynchronous suspension>

Dependencies:

video_player_macos:
    git:
      url: https://github.com/ollydixon/flutter_macos_video_player
      path: packages/video_player/video_player_macos
  video_player:
    git:
      url: https://github.com/ollydixon/flutter_macos_video_player
      path: packages/video_player/video_player