nativeaudio

commit d5dde756fc3200d476325eda5c69f54e6ff9b4d4
parent bf19fbe42f8f291e04a1ded34c3261a5c18007c3
Author: Jack Mordaunt <jackmordaunt.dev@gmail.com>
Date:   Fri, 18 Sep 2026 13:16:18 -0400

mf: pin the decoder output to 16 bits per sample

Asking the source reader only for PCM lets it hand back whatever width
the source uses, so a 24-bit WAV decoded to 24-bit. That breaks the
s16le output the package documents and Format.BytesPerSample promises:
playback rejected it outright, and anything treating the bytes as int16
would have read garbage.

Diffstat:
M
internal/mf/mf.go
 | 
21
+++++++++++++++++++++

1 file changed, 21 insertions(+), 0 deletions(-)
diff --git a/internal/mf/mf.go b/internal/mf/mf.go
@@ -234,6 +234,13 @@ func configureAudioStream(pReader *IMFSourceReader) error {
 		return fmt.Errorf("setting sub type: %w", err)
 	}
 
+	// Pin the sample size. Asking only for PCM lets the reader hand back
+	// whatever width the source happens to use, so a 24-bit file decodes
+	// to 24-bit and breaks the s16le output this package promises.
+	if err := pPartialType.SetUINT32(&MF_MT_AUDIO_BITS_PER_SAMPLE, 16); err != nil {
+		return fmt.Errorf("setting bits per sample: %w", err)
+	}
+
 	// Select the first audio stream, and deselect all other streams.
 	if err := pReader.SetStreamSelection(MF_SOURCE_READER_ALL_STREAMS, false); err != nil {
 		return fmt.Errorf("deselecting audio streams: %w", err)
@@ -776,6 +783,20 @@ func (v *IMFMediaType) SetGUID(guid *GUID, value *GUID) error {
 	return nil
 }
 
+// SetUINT32 stores an unsigned 32-bit attribute on the media type.
+func (v *IMFMediaType) SetUINT32(guid *GUID, value uint32) error {
+	r, _, _ := syscall.SyscallN(
+		v.VTable.SetUINT32,
+		uintptr(unsafe.Pointer(v)),
+		uintptr(unsafe.Pointer(guid)),
+		uintptr(value),
+	)
+	if r != S_OK {
+		return MFErr{Code: r}
+	}
+	return nil
+}
+
 func (v *IMFMediaType) GetUINT32(guid *GUID, punValue *uint32) error {
 	r, _, _ := syscall.SyscallN(
 		v.VTable.GetUINT32,