Add failing test coverage of regressing video scenario

osu.Game.Tests/Beatmaps/Formats/LegacyStoryboardDecoderTest.cs

@@ -306,6 +306,29 @@ namespace osu.Game.Tests.Beatmaps.Formats
             }
         }
 
+        [Test]
+        public void TestVideoWithCustomFadeIn()
+        {
+            var decoder = new LegacyStoryboardDecoder();
+
+            using var resStream = TestResources.OpenResource("video-custom-alpha-transform.osb");
+            using var stream = new LineBufferedReader(resStream);
+
+            var storyboard = decoder.Decode(stream);
+
+            Assert.Multiple(() =>
+            {
+                Assert.That(storyboard.GetLayer(@"Video").Elements, Has.Count.EqualTo(1));
+                Assert.That(storyboard.GetLayer(@"Video").Elements.Single(), Is.InstanceOf<StoryboardVideo>());
+                Assert.That(storyboard.GetLayer(@"Video").Elements.Single().StartTime, Is.EqualTo(-5678));
+                Assert.That(((StoryboardVideo)storyboard.GetLayer(@"Video").Elements.Single()).Commands.Alpha.Single().StartTime, Is.EqualTo(1500));
+                Assert.That(((StoryboardVideo)storyboard.GetLayer(@"Video").Elements.Single()).Commands.Alpha.Single().EndTime, Is.EqualTo(1600));
+
+                Assert.That(storyboard.EarliestEventTime, Is.Null);
+                Assert.That(storyboard.LatestEventTime, Is.Null);
+            });
+        }
+
         [Test]
         public void TestVideoAndBackgroundEventsDoNotAffectStoryboardBounds()
         {

osu.Game.Tests/Resources/video-custom-alpha-transform.osb

@@ -0,0 +1,5 @@
+osu file format v14
+
+[Events]
+Video,-5678,"Video.avi",0,0
+ F,0,1500,1600,0,1