Move movie runtime support to frontend

engine/Age.Engine.Frontend/MovieRuntime.cs

@@ -0,0 +1,35 @@
+using System;
+using System.Diagnostics;
+using Age.Engine.Sys4;
+
+/// <summary>Presentation-side ownership for one decoder plus its fail-safe completion deadline.</summary>
+internal sealed record MovieRuntime(string Name, int AssetId, long ResourceId, IMovieDecoder Decoder,
+                                    long MovieFlags, long InitialPositionMs,
+                                    long StartedAtTimestamp, long StartDelayMs,
+                                    long? PresentationDurationMs, long WatchdogMs)
+{
+    public static MovieRuntime Open(string name, int assetId, long resourceId, MoviePayload payload,
+                                    IMovieDecoderFactory factory, long movieFlags = 0,
+                                    long initialPositionMs = 0, long startDelayMs = 0,
+                                    long? presentationDurationMs = null)
+    {
+        ArgumentNullException.ThrowIfNull(factory);
+        long safeDelayMs = Math.Max(0, startDelayMs);
+        long? safeDurationMs = presentationDurationMs is >= 0
+            ? Math.Max(0, presentationDurationMs.Value)
+            : null;
+        IMovieDecoder decoder = factory.Open(
+            payload, Math.Max(0, initialPositionMs), safeDurationMs);
+        long remainingMs = decoder.StopTimeMs is >= 0 and var stopTime
+            ? Math.Max(0, stopTime - decoder.InitialPositionMs)
+            : -1;
+        long watchdogBasis = safeDurationMs ?? remainingMs;
+        if (watchdogBasis >= 0) watchdogBasis = checked(watchdogBasis + safeDelayMs);
+        return new MovieRuntime(name, assetId, resourceId, decoder, movieFlags,
+            decoder.InitialPositionMs, Stopwatch.GetTimestamp(),
+            safeDelayMs, safeDurationMs,
+            watchdogBasis >= 0
+                ? Math.Clamp(watchdogBasis + 2000, 5000, 300000)
+                : 30000);
+    }
+}