feat: validate availability of native Windows libraries

Validate whether the native libraries and their linked dependencies (e.g., MSVC runtime) are available and throw helpful error in case something is missing.

src/Aurio.FFmpeg/FFmpegAudioStreamFactory.cs

@@ -24,6 +24,11 @@ namespace Aurio.FFmpeg
 {
     public class FFmpegAudioStreamFactory : IAudioStreamFactory
     {
+        public FFmpegAudioStreamFactory()
+        {
+            FFmpegReader.ValidateNativeLibraryAvailability();
+        }
+
         public IAudioStream OpenFile(FileInfo fileInfo, FileInfo proxyFileInfo = null)
         {
             if (FFmpegSourceStream.WaveProxySuggested(fileInfo))

src/Aurio.FFmpeg/FFmpegReader.cs

@@ -45,6 +45,8 @@ public class FFmpegReader : IDisposable
         /// <param name="mode">the types of data to read</param>
         public FFmpegReader(string filename, Type mode)
         {
+            ValidateNativeLibraryAvailability();
+
             this.filename = filename;
             this.mode = mode;
 
@@ -75,6 +77,8 @@ public FFmpegReader(FileInfo fileInfo, Type mode)
         /// <param name="fileName">optional filename as a hint for FFmpeg to determine the data format</param>
         public FFmpegReader(Stream stream, Type mode, string fileName)
         {
+            ValidateNativeLibraryAvailability();
+
             this.filename = fileName ?? "bufferedIO_stream";
             this.mode = mode;
 
@@ -131,6 +135,36 @@ public FFmpegReader(Stream stream, Type mode, string fileName)
         public FFmpegReader(Stream stream, Type mode)
             : this(stream, mode, null) { }
 
+        public static void ValidateNativeLibraryAvailability()
+        {
+            IntPtr dummyInstance = Marshal.AllocHGlobal(100);
+
+            try
+            {
+                // This can be any native invocation
+                InteropWrapper.stream_has_error(dummyInstance);
+            }
+            catch (DllNotFoundException e)
+            {
+                if (OperatingSystem.IsWindows())
+                {
+                    throw new DllNotFoundException(
+                        "The native FFmpeg proxy library cannot be loaded. Please make sure that the "
+                            + "Microsoft Visual C++ Redistributable for Visual Studio 2015 (or later) is installed.",
+                        e
+                    );
+                }
+                else
+                {
+                    throw;
+                }
+            }
+            finally
+            {
+                Marshal.FreeHGlobal(dummyInstance);
+            }
+        }
+
         private void CheckAndHandleOpeningError()
         {
             if (InteropWrapper.stream_has_error(instance))

src/Aurio.Soxr/ResamplerFactory.cs

@@ -22,6 +22,11 @@ namespace Aurio.Soxr
 {
     public class ResamplerFactory : IResamplerFactory
     {
+        public ResamplerFactory()
+        {
+            SoxResampler.ValidateNativeLibraryAvailability();
+        }
+
         public IResampler CreateInstance(
             ResamplingQuality quality,
             int channels,

src/Aurio.Soxr/SoxResampler.cs

@@ -53,6 +53,8 @@ public class SoxResampler : IDisposable
             QualityFlags qualityFlags
         )
         {
+            ValidateNativeLibraryAvailability();
+
             if (inputRate <= 0 || outputRate <= 0 || channels <= 0)
             {
                 throw new SoxrException("one or more parameters are invalid (zero or negative)");
@@ -133,6 +135,30 @@ public SoxResampler(double inputRate, double outputRate, int channels)
                 QualityFlags.SOXR_ROLLOFF_SMALL
             ) { }
 
+        public static void ValidateNativeLibraryAvailability()
+        {
+            try
+            {
+                // This can be any native invocation
+                InteropWrapper.soxr_version();
+            }
+            catch (DllNotFoundException e)
+            {
+                if (OperatingSystem.IsWindows())
+                {
+                    throw new DllNotFoundException(
+                        "The native Soxr library cannot be loaded. Please make sure that the "
+                            + "Microsoft Visual C++ Redistributable for Visual Studio 2015 (or later) is installed.",
+                        e
+                    );
+                }
+                else
+                {
+                    throw;
+                }
+            }
+        }
+
         /// <summary>
         /// Returns the libsoxr version.
         /// </summary>