test/CustomMoviePlayer.cs
using Sandbox.MovieMaker;

public sealed class CustomMoviePlayer : Component
{
	[Property] public MoviePlayer Player { get; set; }

	public void Play()
	{
		Player.IsPlaying = true;
		Log.Info( "playing!" );
	}

	public void Stop()
	{
		Player.IsPlaying = false;
	}
}