From 1cf4ccd05bfd510cf17a0d9468ab75ebfb465625 Mon Sep 17 00:00:00 2001
From: Nikolaj Olsson <nikse.dk@gmail.com>
Date: Sun, 17 Nov 2024 21:13:58 +0100
Subject: [PATCH] Allow reading matroska files with "mp4" ext Related to #9010

---
 src/libse/Common/FileUtil.cs | 12 ++++++++++++
 src/ui/Forms/Main.cs         |  7 ++++++-
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/src/libse/Common/FileUtil.cs b/src/libse/Common/FileUtil.cs
index 2ac9056e1..6565a7ebe 100644
--- a/src/libse/Common/FileUtil.cs
+++ b/src/libse/Common/FileUtil.cs
@@ -859,6 +859,18 @@ namespace Nikse.SubtitleEdit.Core.Common
             }
         }
 
+        public static bool IsMatroskaFileFast(string fileName)
+        {
+            using (var fs = new FileStream(fileName, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
+            {
+                var buffer = new byte[4];
+                fs.Read(buffer, 0, buffer.Length);
+
+                // 1a 45 df a3
+                return buffer[0] == 0x1a && buffer[1] == 0x45 && buffer[2] == 0xdf && buffer[3] == 0xa3;
+            }
+        }
+
         /// <summary>
         /// Checks if a file is locked by attempting to open it with exclusive read access.
         /// </summary>
diff --git a/src/ui/Forms/Main.cs b/src/ui/Forms/Main.cs
index e0e1f01f4..7bd115b15 100644
--- a/src/ui/Forms/Main.cs
+++ b/src/ui/Forms/Main.cs
@@ -2952,7 +2952,12 @@ namespace Nikse.SubtitleEdit.Forms
                 }
             }
 
-            if (ext == ".mkv" || ext == ".mks")
+            if (ext == ".mkv" || ext == ".mks" ||
+
+                // allow for mkv files with wrong extension
+                ((ext == ".mp4" || ext == ".mov" || ext == ".m4v" || ext == ".wmv") && FileUtil.IsMatroskaFileFast(fileName) && FileUtil.IsMatroskaFile(fileName))
+                
+                ) 
             {
                 ImportSubtitleFromMatroskaFile(fileName);
                 return;