From 13a2f09d2436269edb7f33ccbcc6bad7a31694c3 Mon Sep 17 00:00:00 2001
From: Tim Horemans <tim.horemans@tenforce.com>
Date: Wed, 30 Oct 2024 12:01:47 +0100
Subject: [PATCH] Retrieve error text for MmResult in MmException

---
 NAudio.Core/MmException.cs | 28 +++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/NAudio.Core/MmException.cs b/NAudio.Core/MmException.cs
index 26dd5d05..e7143a43 100644
--- a/NAudio.Core/MmException.cs
+++ b/NAudio.Core/MmException.cs
@@ -1,4 +1,6 @@
 using System;
+using System.Runtime.InteropServices;
+using System.Text;
 
 namespace NAudio
 {
@@ -19,10 +21,34 @@ public MmException(MmResult result, string function)
             Function = function;
         }
 
+        private const int ErrorTextMaxLength = 256;
+
+        // https://learn.microsoft.com/en-us/windows/win32/api/mmeapi/nf-mmeapi-waveoutgeterrortext
+        /// <summary>
+        /// The waveOutGetErrorText function retrieves a textual description of the error identified by the given error number.
+        /// </summary>
+        /// <param name="mmrError">Error number.</param>
+        /// <param name="pszText">Pointer to a buffer to be filled with the textual error description.</param>
+        /// <param name="cchText">Size, in characters, of the buffer pointed to by pszText.</param>
+        /// <returns>Returns MMSYSERR_NOERROR if successful or an error otherwise.</returns>
+        [DllImport("winmm.dll", CharSet = CharSet.Auto)]
+        private static extern MmResult waveOutGetErrorText(MmResult mmrError, StringBuilder pszText, uint cchText);
+
+        private static string GetErrorText(MmResult result)
+        {
+            var sb = new StringBuilder(ErrorTextMaxLength);
+            var textResult = waveOutGetErrorText(result, sb, ErrorTextMaxLength);
+            if (textResult == MmResult.NoError)
+            {
+                return sb.ToString();
+            }
+
+            return textResult.ToString();
+        }
 
         private static string ErrorMessage(MmResult result, string function)
         {
-            return $"{result} calling {function}";
+            return $"{result} calling {function}: {GetErrorText(result)}";
         }
 
         /// <summary>