ADOFAIRenderer/Patch/Game/scnGamePatch.cs

using System.IO;
using ADOFAIRenderer.Core;
using ADOFAIRenderer.Util;
using HarmonyLib;

namespace ADOFAIRenderer.Patch.Game
{
    [HarmonyPatch(typeof(scnGame))]
    // ReSharper disable once InconsistentNaming
    public static class scnGamePatch
    {
        [HarmonyPrefix]
        [HarmonyPatch("UpdateVideo")]
        public static bool Prefix(scnGame __instance)
        {
            // Only replace when rendering is active
            if (!RenderManager.IsActive)
            {
                // Remove FFmpeg player if it was attached previously
                var oldPlayer = __instance.videoBG.gameObject.GetComponent<FFmpegVideoBGPlayer>();
                if (oldPlayer != null)
                {
                    UnityEngine.Object.Destroy(oldPlayer);
                }
                // Re-enable native player component
                __instance.videoBG.enabled = true;
                return true; // Execute original
            }

            string text = __instance.levelData.miscSettings.GetString("bgVideo");
            if (string.IsNullOrEmpty(text))
            {
                __instance.videoBG.gameObject.SetActive(false);
                return false; // Skip original
            }

            __instance.videoBG.gameObject.SetActive(true);

            // We can only play external video files via FFmpegNativeDecoder.
            // Internal/Bundle level background videos are built-in VideoClips, so we fallback to native Unity VideoPlayer.
            if (ADOBase.isInternalLevel || ADOBase.isBundleLevel)
            {
                __instance.videoBG.enabled = true;
                return true; // Execute original
            }

            // Custom level video path
            string videoPath = Path.Combine(Path.GetDirectoryName(ADOBase.levelPath), text);
            if (!File.Exists(videoPath))
            {
                return true; // Let the original print error
            }

            // Disable native VideoPlayer component (to prevent it from attempting real-time playback and sync errors)
            __instance.videoBG.enabled = false;

            // Add or retrieve our custom FFmpeg video background player
            var player = __instance.videoBG.gameObject.GetComponent<FFmpegVideoBGPlayer>();
            if (player == null)
            {
                player = __instance.videoBG.gameObject.AddComponent<FFmpegVideoBGPlayer>();
            }

            bool isLooping = __instance.levelData.miscSettings.GetBool("loopVideo");
            
            // In custom levels, ADOFAI's videoBG targetTexture is pre-allocated by the game to render background filters.
            // We initialize the player with the target RenderTexture.
            player.Init(videoPath, __instance.videoBG.targetTexture, isLooping);

            return false; // Skip original UpdateVideo
        }
    }
}