Add isolated FFmpeg movie decoder shim

godot/IMovieDecoder.cs

@@ -0,0 +1,25 @@
+using System;
+using System.Runtime.Versioning;
+using Age.Engine.Sys4;
+
+/// <summary>
+/// Platform-neutral movie playback boundary. Construction is synchronous so metadata needed by the VM is
+/// available before op 0x236 returns; frame delivery and completion remain asynchronous.
+/// </summary>
+internal interface IMovieDecoder : IDisposable
+{
+    long? StopTimeMs { get; }
+    bool IsCompleted { get; }
+    bool TryTakeFrame(out RgbaImage frame);
+}
+
+internal interface IMovieDecoderFactory
+{
+    IMovieDecoder Open(MoviePayload movie);
+}
+
+[SupportedOSPlatform("windows")]
+internal sealed class DirectShowMovieDecoderFactory : IMovieDecoderFactory
+{
+    public IMovieDecoder Open(MoviePayload movie) => new DirectShowMovieDecoder(movie);
+}