Fix Windows libmpv search paths

src/ui/Logic/VideoPlayers/LibMpvDynamic/LibMpvDynamicPlayer.cs

@@ -365,16 +365,57 @@ private static string[] GetLibraryNames()
         }
     }
 
+    internal static string[] GetWindowsLibraryPaths(
+        string mpvPath,
+        string dataFolder,
+        string baseDirectory,
+        string currentDirectory)
+    {
+        var paths = new List<string>();
+        var comparisonPaths = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
+
+        void AddPath(string path)
+        {
+            if (string.IsNullOrEmpty(path))
+            {
+                if (comparisonPaths.Add(string.Empty))
+                {
+                    paths.Add(path);
+                }
+
+                return;
+            }
+
+            var comparisonPath = Path.TrimEndingDirectorySeparator(Path.GetFullPath(path));
+            if (comparisonPaths.Add(comparisonPath))
+            {
+                paths.Add(path);
+            }
+        }
+
+        // A configured override wins. The per-user data folder comes next so a downloaded
+        // libmpv can override the installer/portable baseline without administrator rights.
+        if (!string.IsNullOrWhiteSpace(mpvPath))
+        {
+            AddPath(mpvPath);
+        }
+
+        AddPath(dataFolder);
+        AddPath(baseDirectory);
+        AddPath(currentDirectory);
+        AddPath(string.Empty);
+        return paths.ToArray();
+    }
+
     private static string[] GetLibraryPaths()
     {
         if (OperatingSystem.IsWindows())
         {
-            return
-            [
+            return GetWindowsLibraryPaths(
                 MpvPath,
-                Directory.GetCurrentDirectory(),
-                string.Empty,
-            ];
+                Se.DataFolder,
+                AppContext.BaseDirectory,
+                Directory.GetCurrentDirectory());
         }
         else if (OperatingSystem.IsLinux())
         {
@@ -456,23 +497,32 @@ private void LoadLibMpvMethods()
         return address != IntPtr.Zero ? Marshal.GetDelegateForFunctionPointer(address, type) : null;
     }
 
+    internal static bool ShouldAttemptLibraryLoad(string libraryPath, string fullPath)
+    {
+        // The empty Windows root is a sentinel for the platform loader's normal search path.
+        // Do not pre-empt that fallback with File.Exists(), which only checks the process CWD.
+        return string.IsNullOrEmpty(libraryPath) || File.Exists(fullPath);
+    }
+
     private bool LoadLibraryInternal()
     {
         foreach (var libName in GetLibraryNames())
         {
             foreach (var libPath in GetLibraryPaths())
             {
                 var fullPath = Path.Combine(libPath, libName);
-                if (File.Exists(fullPath))
+                if (!ShouldAttemptLibraryLoad(libPath, fullPath))
                 {
-                    var libHandle = NativeMethods.CrossLoadLibrary(fullPath);
-                    if (libHandle != IntPtr.Zero)
-                    {
-                        _library = libHandle;
-                        LoadLibMpvMethods();
-                        _mpv = _mpvCreate!.Invoke();
-                        return true;
-                    }
+                    continue;
+                }
+
+                var libHandle = NativeMethods.CrossLoadLibrary(fullPath);
+                if (libHandle != IntPtr.Zero)
+                {
+                    _library = libHandle;
+                    LoadLibMpvMethods();
+                    _mpv = _mpvCreate!.Invoke();
+                    return true;
                 }
             }
         }

tests/UI/Logic/VideoPlayers/LibMpvLibraryPathTests.cs

@@ -0,0 +1,76 @@
+using Nikse.SubtitleEdit.Logic.VideoPlayers.LibMpvDynamic;
+
+namespace UITests.Logic.VideoPlayers;
+
+/// <summary>
+/// The Windows installer and the in-app updater keep libmpv in different roots. Library lookup
+/// must name those roots explicitly instead of depending on the process working directory.
+/// </summary>
+public class LibMpvLibraryPathTests
+{
+    [Fact]
+    public void GetWindowsLibraryPaths_PutsManualOverrideFirst()
+    {
+        var paths = LibMpvDynamicPlayer.GetWindowsLibraryPaths("/manual", "/data", "/app", "/cwd");
+
+        Assert.Equal("/manual", paths[0]);
+    }
+
+    [Fact]
+    public void GetWindowsLibraryPaths_PutsDownloadedCopyBeforeBundledCopy()
+    {
+        var paths = LibMpvDynamicPlayer.GetWindowsLibraryPaths(string.Empty, "/data", "/app", "/cwd");
+
+        Assert.Equal("/data", paths[0]);
+        Assert.Equal("/app", paths[1]);
+    }
+
+    [Fact]
+    public void GetWindowsLibraryPaths_DoesNotDependOnWorkingDirectoryForKnownCopies()
+    {
+        var paths = LibMpvDynamicPlayer.GetWindowsLibraryPaths(string.Empty, "/data", "/app", "/cwd");
+
+        Assert.True(Array.IndexOf(paths, "/data") < Array.IndexOf(paths, "/cwd"));
+        Assert.True(Array.IndexOf(paths, "/app") < Array.IndexOf(paths, "/cwd"));
+        Assert.Equal(string.Empty, paths[^1]);
+    }
+
+    [Fact]
+    public void GetWindowsLibraryPaths_DeduplicatesPortableRoots()
+    {
+        var paths = LibMpvDynamicPlayer.GetWindowsLibraryPaths(string.Empty, "/portable", "/portable", "/portable");
+
+        Assert.Equal(["/portable", string.Empty], paths);
+    }
+    [Fact]
+    public void GetWindowsLibraryPaths_DeduplicatesEquivalentRootsWithTrailingSeparator()
+    {
+        var root = Path.Combine(Path.GetTempPath(), "libmpv-path-test");
+        var rootWithSeparator = root + Path.DirectorySeparatorChar;
+
+        var paths = LibMpvDynamicPlayer.GetWindowsLibraryPaths(string.Empty, rootWithSeparator, root, root);
+
+        Assert.Equal([rootWithSeparator, string.Empty], paths);
+    }
+
+
+    [Fact]
+    public void ShouldAttemptLibraryLoad_DefaultLoaderSentinel_DoesNotRequireLocalFile()
+    {
+        var missing = Path.Combine(Path.GetTempPath(), "missing-" + Guid.NewGuid().ToString("N"), "libmpv-2.dll");
+
+        Assert.False(File.Exists(missing));
+        Assert.True(LibMpvDynamicPlayer.ShouldAttemptLibraryLoad(string.Empty, missing));
+    }
+
+    [Fact]
+    public void ShouldAttemptLibraryLoad_ExplicitRoot_RequiresExistingFile()
+    {
+        var missing = Path.Combine(Path.GetTempPath(), "missing-" + Guid.NewGuid().ToString("N"), "libmpv-2.dll");
+
+        Assert.False(File.Exists(missing));
+        Assert.False(LibMpvDynamicPlayer.ShouldAttemptLibraryLoad(Path.GetDirectoryName(missing)!, missing));
+    }
+
+
+}