Add Custom Frame Modification Hook API for Video Rendering

API/IFrameHook.cs

@@ -0,0 +1,24 @@
+using System.Diagnostics.CodeAnalysis;
+
+namespace ADOFAIRenderer.API;
+
+/// <summary>
+/// Represents a custom frame modification hook that can modify rendered frames using GPU ping-pong double buffering.
+/// </summary>
+/// <remarks>
+/// <b>Execution Frequency Note:</b> Frame hooks are only invoked for frames that are actually encoded into the final video (<c>VideoFPS</c>).
+/// When <c>RenderFPS</c> is higher than <c>VideoFPS</c>, intermediate game render frames are skipped and this hook
+/// will <b>not</b> be called on every game frame.
+/// </remarks>
+[SuppressMessage("ReSharper", "UnusedType.Global")]
+public interface IFrameHook
+{
+    /// <summary>
+    /// Invoked for each captured video frame before it is encoded.
+    /// </summary>
+    /// <remarks>
+    /// This method is not called on every rendered game frame if <c>RenderFPS</c> exceeds <c>VideoFPS</c>.
+    /// </remarks>
+    /// <param name="context">The frame hook context providing access to ping-pong textures and frame metadata.</param>
+    void OnRenderFrame(FrameHookContext context);
+}