A feature and tidy-up release. Its headline is a first preview of macOS support: the new NAudio.MacOS package wraps Core Audio for playback and recording, Extended Audio File Services for reading and writing compressed formats, and AudioConverter for resampling. It ships pre-release only while its API settles, alongside the stable versions of the other packages. VB.NET users also get base classes and a guide that keep the NAudio 2 array-based Read signature.

Several legacy APIs that have modern replacements are now [Obsolete], to be removed in the next major version. The fixes include DirectSoundOut, which failed every playback in 3.1.0, and WasapiPlayer/WasapiOut getting stuck in the Playing state after a source error.

• macOS support (preview) - A new wrappers library is added wrapping macOS native API's for playback/recording, reading/writing files and resampling audio. The NAudio.MacOS package ships pre-release only (X.Y.Z-preview.N) while its API settles, so it stays pre-release alongside stable releases of the other packages. Special thanks to @mdcdi1315 (#1325) for the work and the tests. For more information, see the design doc that describes the decisions that helped shape the wrappers. (#1398)
• VB.NET support - Added SampleProviderBase and WaveProviderBase, base classes that keep the NAudio 2 Read(buffer, offset, count) signature for languages that cannot name a Span<T> in a method signature, and a Using NAudio from VB.NET guide covering playback, recording and custom providers from VB (#1426)
• Deprecated legacy APIs that have modern replacements: Wave16ToFloatProvider, WaveFloatTo16Provider and Wave32To16Stream (use ToSampleProvider() / ToWaveProvider16()), IgnoreDisposeStream (no longer needed), ByteArrayExtensions (use the BCL), MidiMessage (use the typed MIDI events), ResamplerDmoStream/DmoResampler (use MediaFoundationResampler or WdlResamplingSampleProvider), DmoEffectWaveProvider and the Dmo* effects (use NAudio.Effects), AsioOut's recording path (use AsioDevice), WaveFilter, and ProgressLog. Added AsioOut.IsSupported() and deprecated the lowercase isSupported() (#1466)
• Deprecated WaveFileReader.ReadNextSampleFrame in favour of ToSampleProvider(), which supports more formats and doesn't allocate an array per sample frame (#1465)
• Reduced allocations when reading and writing WAV files, added ReadOnlySpan<byte> overloads of WaveFileWriter.AddChunk and ChunkIdentifier.ChunkIdentifierToInt32, and fixed WaveChunks.GetData leaving the stream position changed when a read fails. ChunkIdentifierToInt32 now throws ArgumentOutOfRangeException for identifiers that aren't four bytes (#1457)
• Fixed DirectSoundOut failing every playback with DirectSoundException 0x80004001 (or an ArgumentException for a format with extra data, e.g. one read from a WAV by WaveFileReader): the secondary buffer's WAVEFORMATEX was still a GCHandle-pinned WaveFormat instance — a site missed in the #1432 marshalling conversion, since WaveFormat no longer carries [StructLayout] — and now marshals via WaveFormat.MarshalToPtr (#1456)
• Fixed WasapiPlayer and WasapiOut being stranded in the Playing state, unable to play again, when the source's Read threw or the source ended before the first buffer was filled (#1442)
• Fixed WaveFileWriter.WriteSample and WriteSamples(short[]) throwing for plain (non-extensible) 32-bit integer PCM formats (#1463)
• WaveFileReader.ReadNextSampleFrame now throws InvalidDataException for a WAV header with an invalid channel count or bit depth (#1464)
• Changed the WaveStream.CurrentTime setter to clamp to the bounds of the stream, and corrected the XML documentation for the core audio interfaces (#1441)
• Reworked the macOS CoreAudioPlayer and CoreAudioRecorder non-interleaved path, used for devices that expose one mono stream per channel; the recorder now also drains buffered audio when stopped, and non-interleaved streams carrying more than one channel are rejected explicitly (preview) (#1461)
• ExtendedAudioFileServicesReader.CurrentTime and TotalTime on macOS now throw ObjectDisposedException after the reader is disposed, rather than a native exception (preview) (#1451)
• Refreshed the NuGet package icon, now rendered from the new SVG version of the NAudio logo as a sharper, square 256×256 PNG (#1467)
• Fixed the Help and About links in the AudioFileInspector, MidiFileConverter and MixDiff sample apps, which threw on .NET 9 instead of opening the help page or browser, and pointed the links and help pages at GitHub rather than CodePlex (#1469)