feat: .m4a audio file import

OpenUtau.Core/Format/FFmpegWaveReader.cs

@@ -0,0 +1,84 @@
+using System;
+using System.Diagnostics;
+using System.IO;
+using System.Text;
+using NAudio.Wave;
+
+namespace OpenUtau.Core.Format {
+    public class FFmpegWaveReader(string filepath) : WaveStream {
+        private readonly WaveFileReader inner = new(DecodeToMemory(filepath));
+        private static MemoryStream DecodeToMemory(string filepath) {
+            using var proc = new Process {
+                StartInfo = new ProcessStartInfo {
+                    FileName = "ffmpeg",
+                    UseShellExecute = false,
+                    RedirectStandardOutput = true,
+                    RedirectStandardError = true,
+                    CreateNoWindow = true,
+                }
+            };
+            proc.StartInfo.ArgumentList.Add("-i");
+            proc.StartInfo.ArgumentList.Add(filepath);
+            proc.StartInfo.ArgumentList.Add("-f");
+            proc.StartInfo.ArgumentList.Add("wav");
+            proc.StartInfo.ArgumentList.Add("pipe:1");
+            var stderrLog = new StringBuilder();
+            proc.ErrorDataReceived += (_, e) => { if (e.Data != null) stderrLog.AppendLine(e.Data); };
+            try {
+                proc.Start();
+            } catch (Exception) {
+                throw new Exception("ffmpeg not found. Install ffmpeg and ensure it is on PATH.");
+            }
+            proc.BeginErrorReadLine();
+            var memStream = new MemoryStream();
+            proc.StandardOutput.BaseStream.CopyTo(memStream);
+            proc.WaitForExit();
+            if (proc.ExitCode != 0) {
+                throw new Exception($"ffmpeg failed to decode '{Path.GetFileName(filepath)}'.\n{stderrLog}");
+            }
+            // ffmpeg cannot seek back to fix WAV chunk sizes when writing to a non-seekable
+            // pipe, leaving them as 0 or 0xFFFFFFFF. Patch them now that the full size is known.
+            PatchWavHeader(memStream);
+            return memStream;
+        }
+
+        private static void PatchWavHeader(MemoryStream stream) {
+            int total = (int)stream.Length;
+            // Fix RIFF chunk size at offset 4
+            stream.Position = 4;
+            stream.Write(BitConverter.GetBytes(total - 8), 0, 4);
+            // Scan sub-chunks starting after "RIFF" + size + "WAVE"
+            stream.Position = 12;
+            var id = new byte[4];
+            var sz = new byte[4];
+            while (stream.Position <= stream.Length - 8) {
+                stream.Read(id, 0, 4);
+                stream.Read(sz, 0, 4);
+                if (id[0] == 'd' && id[1] == 'a' && id[2] == 't' && id[3] == 'a') {
+                    stream.Position -= 4;
+                    stream.Write(BitConverter.GetBytes(total - (int)stream.Position - 4), 0, 4);
+                    break;
+                }
+                int chunkSize = BitConverter.ToInt32(sz, 0);
+                if (chunkSize < 0) break;
+                stream.Position += chunkSize;
+            }
+            stream.Position = 0;
+        }
+
+        public override WaveFormat WaveFormat => inner.WaveFormat;
+        public override long Length => inner.Length;
+        public override long Position {
+            get => inner.Position;
+            set => inner.Position = value;
+        }
+        public override int Read(byte[] buffer, int offset, int count) => inner.Read(buffer, offset, count);
+
+        protected override void Dispose(bool disposing) {
+            if (disposing) {
+                inner.Dispose();
+            }
+            base.Dispose(disposing);
+        }
+    }
+}

OpenUtau.Core/Format/Wave.cs

@@ -47,6 +47,15 @@ public static WaveStream OpenFile(string filepath) {
             if (ext == ".aiff" || ext == ".aif" || ext == ".aifc") {
                 return new AiffFileReader(filepath);
             }
+            // M4A/AAC: MP4 container has a "ftyp" box at bytes 4–7
+            string ftyp = System.Text.Encoding.ASCII.GetString(buffer.AsSpan(4, 4));
+            if (ftyp == "ftyp" || ext == ".m4a" || ext == ".mp4") {
+#if WINDOWS
+                return new MediaFoundationReader(filepath);
+#else
+                return new FFmpegWaveReader(filepath);
+#endif
+            }
             throw new Exception("Unsupported audio file format.");
         }
 

OpenUtau/FilePicker.cs

@@ -30,7 +30,7 @@ internal class FilePicker {
             Patterns = new[] { "*.musicxml" },
         };
         public static FilePickerFileType AudioFiles { get; } = new("Audio Files") {
-            Patterns = new[] { "*.wav", "*.mp3", "*.ogg", "*.opus", "*.flac" },
+            Patterns = new[] { "*.wav", "*.mp3", "*.ogg", "*.opus", "*.flac", "*.m4a" },
         };
         public static FilePickerFileType WAV { get; } = new("WAV") {
             Patterns = new[] { "*.wav" },

OpenUtau/Views/MainWindow.axaml.cs

@@ -879,7 +879,7 @@ void OnPointerPressed(object? sender, PointerPressedEventArgs args) {
         async void OnDrop(object? sender, DragEventArgs args) {
             string[] ProjectExts = { ".ustx", ".ust", ".vsqx", ".ufdata", ".musicxml", ".mid", ".midi" };
             string[] ArchiveExts = { ".zip", ".rar", ".uar" };
-            string[] AudioExts = { ".mp3", ".wav", ".ogg", ".flac" };
+            string[] AudioExts = { ".mp3", ".wav", ".ogg", ".flac", ".m4a" };
             string[] SupportedExts = ProjectExts
                 .Concat(ArchiveExts)
                 .Concat(AudioExts)