Fix alt version name generation

Instead of replacing all occurrences of the containing folder name, just check the start of the string.
This matches what happens in VideoListResolver.IsEligibleForMultiVersion
Fixes #12555

MediaBrowser.Controller/Entities/BaseItem.cs

@@ -1180,28 +1180,29 @@ namespace MediaBrowser.Controller.Entities
             return info;
         }
 
-        private string GetMediaSourceName(BaseItem item)
+        internal string GetMediaSourceName(BaseItem item)
         {
             var terms = new List<string>();
 
             var path = item.Path;
             if (item.IsFileProtocol && !string.IsNullOrEmpty(path))
             {
+                var displayName = System.IO.Path.GetFileNameWithoutExtension(path);
                 if (HasLocalAlternateVersions)
                 {
-                    var displayName = System.IO.Path.GetFileNameWithoutExtension(path)
-                        .Replace(System.IO.Path.GetFileName(ContainingFolderPath), string.Empty, StringComparison.OrdinalIgnoreCase)
-                        .TrimStart(new char[] { ' ', '-' });
-
-                    if (!string.IsNullOrEmpty(displayName))
+                    var containingFolderName = System.IO.Path.GetFileName(ContainingFolderPath);
+                    if (displayName.Length > containingFolderName.Length && displayName.StartsWith(containingFolderName, StringComparison.OrdinalIgnoreCase))
                     {
-                        terms.Add(displayName);
+                        var name = displayName.AsSpan(containingFolderName.Length).TrimStart([' ', '-']);
+                        if (!name.IsWhiteSpace())
+                        {
+                            terms.Add(name.ToString());
+                        }
                     }
                 }
 
                 if (terms.Count == 0)
                 {
-                    var displayName = System.IO.Path.GetFileNameWithoutExtension(path);
                     terms.Add(displayName);
                 }
             }

tests/Jellyfin.Controller.Tests/Entities/BaseItemTests.cs

@@ -1,4 +1,7 @@
 using MediaBrowser.Controller.Entities;
+using MediaBrowser.Controller.Library;
+using MediaBrowser.Model.MediaInfo;
+using Moq;
 using Xunit;
 
 namespace Jellyfin.Controller.Tests.Entities;
@@ -14,4 +17,30 @@ public class BaseItemTests
     [InlineData("1test 2", "0000000001test 0000000002")]
     public void BaseItem_ModifySortChunks_Valid(string input, string expected)
         => Assert.Equal(expected, BaseItem.ModifySortChunks(input));
+
+    [Theory]
+    [InlineData("/Movies/Ted/Ted.mp4", "/Movies/Ted/Ted - Unrated Edition.mp4", "Ted", "Unrated Edition")]
+    [InlineData("/Movies/Deadpool 2 (2018)/Deadpool 2 (2018).mkv", "/Movies/Deadpool 2 (2018)/Deadpool 2 (2018) - Super Duper Cut.mkv", "Deadpool 2 (2018)", "Super Duper Cut")]
+    public void GetMediaSourceName_Valid(string primaryPath, string altPath, string name, string altName)
+    {
+        var mediaSourceManager = new Mock<IMediaSourceManager>();
+        mediaSourceManager.Setup(x => x.GetPathProtocol(It.IsAny<string>()))
+                .Returns((string x) => MediaProtocol.File);
+        BaseItem.MediaSourceManager = mediaSourceManager.Object;
+
+        var video = new Video()
+        {
+            Path = primaryPath
+        };
+
+        var videoAlt = new Video()
+        {
+            Path = altPath,
+        };
+
+        video.LocalAlternateVersions = [videoAlt.Path];
+
+        Assert.Equal(name, video.GetMediaSourceName(video));
+        Assert.Equal(altName, video.GetMediaSourceName(videoAlt));
+    }
 }